Things to try (in this sequence):
2. Another keyboard
3. Boot into the BIOS and see if the keyboard works there.
4. Boot into a Linux disc or stick (free to make) and see if the keyboard works there.
Please tell your experiences.
The other day i was eating a cheese sandwich, when all of a sudden my keyboard became un-responsive ive tried plugging it in and out of the usb port but no joy, just wondering what is wrong with it, i think my PC might be ready for the bin, its a desktop. (PS Im writing this from my work PC)