Firstly, I presume you have rebooted the machine before all this? ie controlled shutdown and proper cold start.

Second thing to is to check you haven't got rubbish under the keys - it's often the case.

Keyboard upside down, bit of blowing, hit the keys hard etc

Try an ALT-[key] combination and see if it works
Try an CTR-[key] combination and see if it works
etc