Turned on the computer yesterday only to discover my keyboard wasn't working. Tried to plug it in different ports still didn't work. Uninstalled drivers from device manager, still did not work. Tried other keyboards with the same result. So, on line I went. Some suggested system restore, re-installing drivers, even reinstalling Windows. Another option suggested was to copy this key mentioned from another computer. What I tried; deleting upper and lower filters
So I opened the registration database editor.
Type regedit.exe in the search bar. Open the registry and go to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E96B-E325-11CE-BFC1-08002BE10318}
Click on the little triangle in front of HKEY_LOCAL_MACHINE, then the same for SYSTEM, then CurrentControlSet and so on until you can see the key {4D36E96B-E325-11CE-BFC1-08002BE10318}. Just click on this key to highlight it and then look at the left hand pane.
Look for any line that says UpperFilters and LowerFilters. Right click on them and delete. Before you delete you might want to right-click on the {4D36E96B-E325-11CE-BFC1-08002BE10318} key and export it. This saves a backup of the key and double clicking on it will restore the changes you just made.
Reboot and that should allow your keyboard to work again. Only problem is, I didn't do this. In my case I noticed that instead of the Data section having the name of kbdclass it read keyscrambler kbdclass. I had installed a program called Keyscrambler that wasn't working properly. It was supposed to encrypt your key presses to beat potential keyloggers. I've never had a problem with the program before.
And even when my problems with the program stated it didn't originally interfere with my keyboard but some reason it decided to now. Instead of deleting the key I decided to close down regedit and uninstall keyscrambler first to confirm if that was the issue, and it turned out it was.