F18: Keyboard intermittently not responding

My laptop runs F18 updated from F17 and mostly works on Xfce.

My keyboard occasionally stops responding (even the CapsLk and NumLk won't work).

I can use virtual keyboard to enter, though. And the mouse is fully working.

I believe I can check one of those log files under /var/log, but I am not sure which.

Does anyone have any idea how to do diagnosis on this problem? Thanks.

:)