Not detecting button press at login unless long pressed

The Login screen doesn't accept a word or letter unless it is long pressed. For instance:

Say you want to type 'A', you press A, but it doesnt show it in the screen (if it is a password, no star there).

If you want it to be typed, then you have to pree 'A' and hold for about half a second or more until it appears on the screen.

System Specs:
Dell Inspiron 1545
3 Gb Ram
Ubuntu 11.04 (intalled on June 2011)

PS: This error wasn't present initially. Only after the first System update, it appeared.