Download Keyboard Drivers from manufacturer's website, and follow
installation instructions included with said driver.
-*OR*-
To regain at least basic functionality:
Right click on My Computer
Click on Properties
Click On the Hardware Tab
Click on Device manager
Click on Keyboards
(if not shown then use control panel to Add new hardware)
Click on the plus next to keyboard (if not already expanded)
Right Click on the listed Keyboard
Click on Driver Tab
Click Roll Back Driver if available, see if that works.
If not, click on Update driver and either;
choose a generic keyboard driver or
choose you specific keyboard if listed.
Reboot Computer.
Better?