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USB Troubleshooter

General Guide

The following procedures are general in nature and intended for use by computer professionals or competent, experienced users.  I will not be held responsible for any problems or damages of any kind resulting from the use or misuse of the information posted here.   More Specific Information can be found in the USB Problem Solver

[BIOS] [Cables] [Host Side] [IRQs] [NTKERN.VXD Error] [Non-Intel USB] [Peripherals] [Older Systems] [PCI/USB] [Special Section]

USB Host Side Issues

USB Connectivity Requirements

To achieve proper USB connectivity six basic system elements must be present and working correctly.

1)  Support from the BIOS

2)  Support from the Operating System

3)  Physical USB ports

4)  A USB Device

5)  The correct USB cable for the device

6)  Drivers either from the OS and/or the peripheral maker

Does my Computer Support USB?

There are two programs available to check if your system is USB ready.  Although, neither of these programs is a guarantee that your computer will provide trouble-free USB, both provide good indications of capability.

Identify the USB Host Controller   

All USB host controllers are NOT created equal.  You should identify the USB host controller type so that you will know how to proceed if you have problems.  For a  “How To”, go here:

Cleanup the Device Manager / Windows Safe Mode    

From initial installation problems to suddenly not working USB, cleaning up the Device Manager in Safe mode is the first step in Win9X troubleshooting.  Many hardware related problems in Windows can be traced to ghost and/or duplicate device entries.  Obsolete and/or duplicate devices can ONLY be seen and removed from the Device Manager while in Windows Safe Mode.  For a good  “How To”, see here:

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BIOS Settings

Common BIOS Problems

Many USB Problems are the result of improper settings in the BIOS.  To achieve proper USB connectivity the BIOS needs to be a properly working partner. 

Enable USB in the BIOS

USB is often disabled by Default in the BIOS.  To enable USB in the BIOS one or more of the following statements must be true.   

  • USB Keyboard - DOS or Enabled (Even if you have NO USB Keyboard)

  • Legacy USB Support - Enabled


  • Assign IRQ for USB - Enabled (Some combinations of OS and BIOS version require this setting to be Disabled).    

If there are NO references to USB in the BIOS setup, your BIOS Version Needs To Be Updated.

The BIOS version does NOT support USB.  

Vintage 1996-97 motherboards, even those with USB pinouts (AT Style) almost always require a BIOS update to achieve proper USB connectivity.  Generally, a BIOS date of June 1998 or newer is required for Win9x systems.  A BIOS date of October 1999 or newer is usually required for systems running Windows 2000.  New Operating Systems require new BIOS revisions.

BIOS Help Links

  • BIOS Agent - Free Software Reports Your BIOS Details and Configuration

  • BadFlash - Good Information and Help

  • CTBIOS - Small DOS program that identifies the BIOS and motherboard - Program is in German but, you'll get the idea

  • Wim's Bios Page - BIOS Help Site

  • USBMan BIOS Download Site - Listed by Manufacturer

  • Improperly updating the BIOS can render a system inoperable and unbootable.  Follow ALL manufacturers instructions carefully when updating the BIOS.  Clear the CMOS with the jumper (see manual) and reset all BIOS data before rebooting to Windows. 

BIOS settings Effecting USB

BIOS settings that effect the operation of Universal Serial Bus are shown optimized for USB.  The most common BIOS settings that effect USB performance are:


  • Reset the FSB to Default

Aggressive memory settings (Turbo/Fast)

  • Reset to Normal or Default

Lack of usable IRQs

  • Com1 and Com2 can be disabled if not used, allowing the OS to use these IRQs for other devices.

Plug and Play OS – Disabled 

  • Older Win9x (Socket 7 based) systems may require this option to be Enabled to allow Windows controlled IRQ Steering to operate correctly.  Toggle ON or OFF as your system requires.

IRQs Assigned – Auto

Power Management – Disabled 

  • The Operating System should control Power Management.  

ACPI - Disabled 

  • ACPI enabled in the BIOS is the source of many USB problems.  If you are having problems with USB, ACPI should be disabled.  Unfortunately, simply resetting the switch in the BIOS may not be enough.  Normally, a reinstall of the operating system will be necessary.  Remember to backup your data before you reinstall the OS.  I recommend a clean install to a newly formatted hard drive.

USB Keyboard – Enabled or DOS

Assign IRQ for USB – This setting varies by motherboard type.  The “rule of thumb” is, Enabled for Win2000 and Disabled for Win9X.  Try both settings if you are having problems.

BIOS Date 

If you are installing USB for the first time a BIOS update may be needed, especially if your motherboard is vintage 1996-97.  The leading cause of USB failure in these motherboards is a BIOS version that predates Win98, June 1998.  If you are unable to update the BIOS to June 1998 or later, your chances of installing correctly working USB is greatly diminished. 

For more information on determining your motherboard type and updating your BIOS go here:

Once you have identified your motherboard, go to the manufacturer’s web site and check for a BIOS update.  Most Mainboard manufacturers are listed here: 

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IRQ Steering    

Properly installed IRQ Steering is critical to correctly working USB.  If IRQ Steering is disabled the likely cause is improper BIOS settings.  See the section on BIOS Settings.  To see what properly installed IRQ Steering looks like, go here:


IRQ Conflicts with USB

Despite information to the contrary, USB does NOT like to share its IRQ with another device, (IRQ Holder for PCI Steering is not considered another device).

If USB is sharing its IRQ with Audio, Video, NIC or Modem you will very likely have problems with USB.  (All OS except WinXP)

Free as many IRQs as possible in the BIOS.  A good place to start is COM1 and/or COM2 if you have no external serial device attached to your computer.  (i.e Serial Mouse or Digital Camera)  If you are using a USB printer you can also Disable the Parallel port.

After disabling devices in the BIOS, you must boot into Windows Safe Mode and delete the device from the Windows Device Manager (Win95-Win2000).  If the device is not removed from the Windows Device Manager while in Safe Mode, Windows will continue to recognize the device and assign it an IRQ.

Moving peripheral cards to other available slots is also an effective method of resolving IRQ conflicts.  Each PCI slot is assigned an IRQ by Default.  Some PCI slots share an IRQ with USB.  Avoid those slots.  Check the Mainboard Owners Manual for this information and use it as a guide to avoid IRQ conflicts.

If freeing IRQs in the BIOS does not produce the desired result you can manually assign an IRQ for a conflicting device in the Windows Device Manager while in Safe Mode.  If manually assigning IRQs you will need to Disable Plug and Play OS in the BIOS, otherwise Windows will continue to override the BIOS assignments.  If the OS is installed in ACPI mode, IRQs assigned in the BIOS will be ignored by the Operating System.  

If you still cannot isolate USB to it’s own IRQ, changing the I/O range of USB sometimes works.

Step-by-Step / William DeVercelly

1. Boot to BIOS setup and disable ACPI
2. Go to the "Integrated Peripherals" section and disable both serial ports if you are not using them.
3. Go to the "PnP/PCI" section and disable "PnP OS", "Auto" and "Reset Configuration Data (aka ESCD Update)". The last is a momentary switch and will be disabled each time you return here. It releases the BIOS lock on IRQs and lets Windows take over.
4. Go to the Power Management section and disable all BIOS control of power management.
5.  Boot DIRECTLY to Windows Safe Mode. Remove all USB software in Add/Remove Programs. Open Device Manager. Remove the USB root hub and host controller *in that order*. Remove all USB drivers. Look for duplicate or erroneous drivers and *remove them all*. Windows will reinstall genuine devices.
6. If you have any SB16 emulation drivers, disable them in the hardware profile (do not remove). These are DOS sound drivers and most don't need them.
7. While still in Safe Mode, go to System Devices and disable Advanced Power Management support.
8. Lastly, remove the drivers for sharing devices. Windows should reinstall the drivers automatically.


Unplug all USB devices except USB Keyboard or Mouse before rebooting to Windows Standard Mode.

At this point you have freed up 2 or 3 IRQs and reset Windows IRQ assignments. You can reboot and reinstall your devices *as per manufacturer's instructions*.



NTKERN.VXD are most often caused when USB cannot negotiate an acceptable IRQ address.  To correct this you will need to free some IRQs in the BIOS and then delete the device entries from the Device Manager while in Windows Safe Mode. (See the IRQ Conflicts Section above)

To Manually reinstall a corrupt VXD File


(For experienced users only.  Backup your data in case a reinstall is necessary)

Specific VXDs are in the CAB files on your Windows installation CD.  VXD files are OS specific.

CAB File Locator












Using Windows Explorer open the Win9X folder on the Windows Installation CD.  Right click on the appropriate CAB file (from above).

Highlight the correct VXD file and extract it to the following Windows folder on the (x) drive that Windows is installed:

Win98 & Win98SE  

  • (x):\Windows\System\VMM32 


  • (x):\Windows\System


  • (x):\System\VMM32 


  • (x):\System32\Drivers

Close Normally and Reboot.  Try the installation again.

Error Code 2 / Robert Biggadike

The NTKERN.VXD device loader(s) for this device could not load the device driver. (Code 2)  

Non-Intel USB Host Controllers (USB Problem Devices) 

Non-Intel and older Intel USB host controllers account for the bulk of problems when a user is trying to establish USB connectivity for the first time.

Tips and Tricks for the most popular non-Intel USB host controllers is here:

USB Problem Guide

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Older Intel USB Host Controllers 

Vintage 1996 - 97 motherboards, even those with USB pinouts, almost always require a BIOS update to achieve proper USB connectivity.  BIOS versions dated before June 1998 usually do NOT provide acceptable USB support.  If the BIOS properly supports USB, installing a motherboard cable assembly will allow you to take advantage of the onboard USB capability of the motherboard.  Go here for information on USB motherboard cable assemblies.  Belkin Model F3U001, Motherboard Cable Assembly has been tested and approved by USBMan for use with most 2 x 4 and 2 x 5, USB pinout arrays.  Go here for more information:  

USB Upgrade Cards

Upgrading to USB by PCI/USB upgrade card is a recommended solution for systems with non-functioning onboard USB host controllers.  A list of tested and approved upgrade cards is here:

Properly Installed the USB upgrade host controller should share the same IRQ as the onboard USB host controller.  Check the motherboard manual or Manufacturers Web Site and install the new card into a PCI Slot that shares it's IRQ with USB.  DO NOT disable USB in the BIOS as the upgrade card may not work if you do.

Make sure that the new upgrade card is fully seated into the PCI slot.  Do not close the case until you have established proper connectivity.

Green ? on Lucent USB Host Controller


Windows 98 & Me Error Message Resource Center


Special Section


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USB Peripherals



  • Improper USB cabling accounts for a high percentage of USB device failure.  Use the cable that was supplied by the manufacturer.  If no cable was supplied with your device, consult the device manual or manufacturer. 

USB is a connectivity solution for peripherals that are in close proximity to the USB host controller (computer).  Cable length must conform to the USB 1.1 Specification.

If your cable is damaged or lost, purchase a certified USB 2.0 cable of the same length or a replacement cable from the manufacturer.  USB 2.0 Certified Cables are the highest quality USB cable available and should work with almost any device except some scanners and cameras that require special shielding. 

Extending USB cabling to a length that is not supported generally results in device failure or unknown device.

Extended length can be achieved by the use of an "active USB cable" or the installation of a powered hub. 

USB over IP Remote I/O Concentrators can be used to extend cable length far beyond the USB 1.1 Specification length. 

Game Controllers


  • USB Hubs connect to the onboard USB host controller and provide additional ports for connecting USB peripheral devices.  A hub does NOT add additional USB bandwidth to the system.  Scanners, web cams, digital cameras, card readers and docking bays are high bandwidth devices that are often not properly supported through a USB hub connection.  If your USB device is NOT recognized or does not work properly, try connecting it to an onboard port.  High bandwidth devices usually require additional USB bandwidth.  If you plan on connecting additional high bandwidth USB devices to your computer you will need to purchase and install either a PCI/USB card (Desktop) or USB CardBus (Laptop) adapter to increase the usable USB bandwidth on your system.  There is a list of Tested and Approved Hubs and PCI/USB cards in the USB Problem Solver under Tools.



  • A USB network can NOT be established by connecting 2 computers using a standard A-A USB cable.  Connecting 2 computers using a standard A-A USB cable will damage both USB ports, the USB peripherals they are attached to and the motherboard.  To establish a USB network you MUST purchase either a USB Direct Connect device or a USB networking kit.  It's always cheaper and often just as easy to use a pair of PCI or ISA NIC cards.



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