see if you can test your KB in safe mode
command prompt. If it still fails then
your kb has a hardware failure. Did you
spill *anything* (even a drop) on your KB?
Did you try to re-seat the kb ribbon?
Keyboards are like speakers, they either
work or they don't. Theres not much else
I can think of unless you are having a
software issue which I doubt you are.

If you don't have any warranty left then
try googling around for a new one or even
ebay. My guess is you may need to replace
it.