It could be any number of reasons. Dirt or something may have gotten inside it. To determine if it is they keyboard or the computer itself, you could get a USB or wireless keyboard and see if that works. IF it does then the laptop keyboard would probably need to be replaced. If an external keyboard does not work it could be driver issues or something more serious. If the computer still boots up and the mouse still works, I’ll bet the keyboard has gone bad. It does happen.