This is a bug
I did find this post through Google, and I must say for all those that are having the same issue:
THIS IS NOT A HARDWARE PROBLEM. THIS IS A WINDOWS 7 (?) BUG.
I just did have the same issue.
I have a DELL Notebook Vostro 1510, and last night everything was working fine. So I turned on my computer today (not from hibernate, but from zero) and for my surprise, none of my keys were working! F1, F2, alphabetical letters, ENTER... none at all.
First thing I decided to do is check if the device was displayed with some kind of issue in "devices manager". All was OK. So I did reboot and still, no keys.
The solution was to UNINSTALL my keyboard device (from the device manager panel) and reboot, making Windows...