Most likely the ribbon cable attaching the keyboard has become detached, probably as a result of not being re-attached properly during a repair. I assume (on boot up) you cannot enter bios by using the Fn keys (usually F2 or F10). If you can, the problem may be software. It's fairly unlikely that a keyboard will fail in it's entirety (usually it's individual keys). Also make sure there's no hardware attached to the laptop which could be disabling the keyboard. Make sure the pointing device (mouse/touch pad) is working. If it isn't the system is frozen maybe (crashed).
Helpful Harry
February 2011
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix notebooks/laptop pcs.