External Kbd not working except in BIOS and Safe Mode

I ran in to a weird situation today on a co-workers laptop. The computer is a Dell E6420. The external Logitech MK710 keyboard stopped working inside windows suddenly this morning. The mouse connected to the same receiver continued to work. The keyboard works inside of Safe mode and in the bios. I have gone through many troubleshooting steps but no external keyboard will not work on the computer while running in Windows. Strangely the quick launch buttons and volume controls still work on the Logitech keyboard but none of the keys work. Also, if the caps lock is pushed on the laptop keyboard the indicator on the MK710 screen will change so communication is occurring between the devices.

The laptop keyboard still works which makes the situation less painful. Here is what I have tried.

1. Replaced batteries since it is wireless.
2. Tried basic known-good Dell USB keyboard. Same results - cannot type in Windows
3. Removed all HID devices from device manager and rebooted.
4. Checked registry HKLM/System/CCS/control/Class and verified keyboard class is set to kbdclass
5. Update BIOS
6. Reset BIOS to defaults after updating.
7. verified regional keyboard settings are set to English - US
8. Disconnected logitech receiver, removed all HID devices again. Plugged in basic USB keyboard again with same result.

I am at my wits end. Any ideas will be greatly appreciated. Thank you.

Hi welcome to the forum

have you tried a restore point before the problem started? you could try a clean boot to see if the keyboard will work. https://support.microsoft.com/en-us/kb/331796

I should have mentioned that. It was the first thing I wanted to try. Somehow system restore was turned off on his computer. I re-enabled it but no restore points prior to this morning.

Oscer, Thank you, thank you!! The link was exactly what I needed to figure it out. I am grateful for a push in the right direction. It turned out to be an old install of HitmanPro.Alert (ver 2.6.5.77 in case someone else has same problem). It had been running happily in the background until today. I went through the list and once that was removed everything is back to normal.

that's good news glad you got it figured out.