Problem solved. There is an option in Universal Access Preferences called "Press and hold keys to accept them (slow keys)". Somehow, that was checked. When I unchecked it, it started working again. I guess accidental pressing of h key must have caused it.
I have a Dell XPS M1530 with Ubuntu 10.04. All was well when the keyboard stopped working all of a sudden. It's working with Vista. When I logon to Ubuntu, it works and lets me login. But it stops working once Gnome is loaded. Mouse/touch screen are working.
I would appreciate any suggestions. I have already tried searching on web but could not find much.
Thanks.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic