How to fix
DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) Error
on Windows

Recently I bought a new USB keyboard and a new USB Mouse. Just after plugging in the devices, I clicked the keyboard, and a BSOD window appeared. The message on it says DRIVER_IRQL_NOT_LESS_OR_EQUAL due to 'kbdclass.sys. After that, I updated all of my drivers, and the problem stopped until I restarted my Windows 8. Once the system logs in, no matter which key I press on the keyboard, the same BSOD appears and then Windows restarts again. Any help would be appreciated.

Thank you for your question and a detailed description of the issue. To start with, we would like to explain what is KBDCLASS.SYS, which is the core of the problem. In fact, KBDCLASS.SYS is a Keyboard Class, which is classified as a driver. It’s responsible for the generic settings within a keyboard, so all combinations that you click, each separate click on keyboards’ keys are handled by KBDCLASS.SYS.

All Windows classes have particular codes. If the class that is being issued is not a system file, then you may not experience problems. However, in this particular case, we are speaking about .sys file, which is a system file. Therefore, if the code of this class gets altered, KBDCLASS.SYS crashes thus causing BSOD and other problems.

In most of the cases, the reason for KBDCLASS.SYS error is Webroot antivirus.[ref en-2] Therefore, if you are using this software utility, try to disable it and check if the BSOD window appears. If disabling this anti-malware helped you to fix DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) error, then the further tips provided on this post are not necessary for you.

If, however, that did not help, it might be that some important settings have been changed on the system, or contrary, some settings that require a change, haven’t been changed. Nevertheless, don’t worry because we are pretty sure that you will fix DRIVER_IRQL_NOT_LESS_OR_EQUAL due to (kbdclass.sys) with our help. In the next paragraph, we will provide several methods that helped other people to get rid of this BSOD.

How to fix DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) on Windows?

Method 1. Fix kbdclass.sys incompatibilities with Webroot anti-virus

It has been found that the core of BSOD DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) error is Webroot antivirus. In other words, the issue arises due to the conflict of the technical features of keyboard class and Webroot software. Luckily, Webroot has been reported about this issue and created a patch for it. Therefore, access the official website of Webroot and check for the patch there.

As soon as you download a patch, close Webroot. For this purpose, right-click on its icon and select Shutdown Protection. If a confirmation window appears, agree to shut down this antivirus. After that, extract a zip file (Webroot’s patch) and click twice on the CompatibilityFlag.reg file.

Method 2. Reset Driver’s changes

It might be that Windows has automatically installed an update for your HID Keyboard Device. Thus, it might be that an automatic update altered the keyboard class code. Therefore, getting back to the previous diver may be the solution. Therefore, you have to:

• Hold Windows key + R.
• Type hdwwiz.cpl and click OK.

  

• Right-click HID Keyboard Device --> Locate Properties --> Driver Tab --> Roll back driver.

If this method was not helpful either, then try the following.

Method 3. Reinstall USB Controllers

To reinstall USB Controllers, you have to uninstall them first. After that, restart the system and the controllers will be reinstalled automatically. To uninstall controllers you have to:

• Hold Windows Key + R.
• Enter hdwwiz.cpl and click OK.
• Find Universal Serial BUS Controllers tab and right-click on the Generic and USB Root Hubs.
• Finally, reboot your PC.

Method 4. Undo some recent system modifications

Try fixing DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) Error by recovering some changes that might have been made to the computer system and provoked the problem to appear:

• Select Start.
• Go to Windows search and type in "System Restore".
• Choose the System Restore option once search results appear.

  

• Follow the provided instructions to choose a restore option.
• Reboot the system.

Method 5. Update Windows if necessary

Maybe you have recently missed some crucial Windows updates that have been the DRIVER_IRQL_NOT_LESS_OR_EQUAL (kbdclass.sys) problem to appear. So, continue by checking if any Windows updates are available and perform the installing if there are some:

• Go to Windows search.
• Find Windows Updates.
• Check for any available updates.

  

• If there are some, click Install Updates.

NOTE: if your system runs into a BSOD like kbdclass.sys, we strongly recommend installing and running a scan with a PC optimization tool. That’s because BSOD errors[ref en-1] may arise due to registries, outdated drivers, cash, and similar problems. Our recommendation would be to use anti-malwar[ref en-3] such as [rev id=”Reimage”].