I agree with Klaus, damage from liquid, or just plain broke. Could be the keyboard itself, or the ribbon cable that connects the keyboard to the motherboard (less likely). Most laptops come apart pretty easily with basic tools and the keyboard can be changed. Check ebay for a new keyboard for your machine. Youtube might have a video on how your specific laptop comes apart. Some older laptops have keyboards that can be removed without pulling the whole laptop apart; there are little clips at the top of the keyboard that can be released with a small flat blade screwdriver, and in some cases a few screws that go through the bottom into the keyboard that hold it in place.