Try following and check after each step -
- Run Keyboard Troubleshooter
Type Troubleshoot in Windows Start Search box > Click Troubleshoot > Scroll down and click Keyboard > Run the troubleshooter > Follow onscreen directions
- Update Keyboard Driver
Windows Key+X (Or right click on Start) > Click Device Manager > Expand Keyboards > Right click on Standard PS/2 Keyboard > Click Update Driver Software > Click Browse my computer for driver software > Click Let my pick from a list of device drivers on my computer > Choose Standard PS/2 Keyboard > Click Next to update
- Turn off filter keys in Ease of Access
Type ease in Windows Start Search box > Click Ease of Access > Click Make the Keyboard easier to use > Ensure Turn on filter Keys is not checked
- Try repairing your Office installation. First try Quick Repair (takes 5 - 10 mins) , if that doesn't help then try Online Repair (Takes more than 30 mins but less than 1 hour in general)
How to repair instructions -