This may be due to water damage or dust, you can buy a replacement keyboard, the old one will just pop out, if you look at the edges of your keyboard you will see tabs, the bottom bigger tabs are fixed and the smaller tabs around the top push in and out. Pry the broken keyboard out, don't worry if you bend it you'll be throwing it away. There is a ribbon cable under the keyboard that connects it to the motherboard, carefully remove it, there may be two tabs either side of the connection, push them gently towards the ribbon and this will release it. Take your new keyboard and connect the ribbon cable to the same motherboard socket, be sure to use the little black tabs to open and then secure the cable. Pop your new keyboard into the tabs and turn your laptop on! Always earth yourself as a precaution while doing repairs of this nature. Make sure you are in a clean environment, there are exposed areas of the motherboard below the keyboard. Do not perform this repair with your laptop on. Best of luck!