Does your keyboard work when you boot into
Safe Mode? Restart your PC and then start pressing F8 as soon as you press the power button. Soon, a menu should appear from which you can use the arrow keys on your keyboard to select
Safe Mode. If your keyboard works here, it could be a keyboard driver issue (especially if you have installed a specialized keyboard in the past).
If your keyboard works in
Safe Mode, open your control panels and click open the system control panel. Click on the hardware tab and then click on the device manager button.
This should open your computer's device manager. There should be an alphabetical list of every device installed on your PC. One of the selections should be "keyboard." Click on the plus sign next to it and remove all installed keyboards.
Restart your PC to exit
Safe Mode and your computer should automatically reinstall your current keyboard using the appropriate drivers. Now, the keyboard should work in normal mode. Post back here after you have tried this so we can know how it went for you.