You can try reconnecting the cable that runs from the keyboard to the laptop's motherboard. If reseating it doesn't help, you most likely have a faulty keyboard that needs replacing (worst case would be a fault on the motherboard).
First, take of the keyboard. You should fin a ribbon cable. It might be slighty disconnected to the motherboard. If so, push it back into place. Then, gently put the keyboard back with all the screws and it might work.
If not, you can get a replacement for fairly cheap.
You might want to plug in a USB/ PS2 keyboard if it doesnt work you can troubleshoot it with windows troubleshoot.