theres a piece of food or something stuck in it. bang it against the table upside down.. if that doesnt work.. you have to flip off the keys and clean. Nah, my bro spilled like a liter of 7up on it accidentally about a year ago and it has been missfunctioning ever since. take pic of keyboard. flip off all the keys, clean with q-tip and hot water. lots of q-tips. or.. cloth. replace keys using pic. see if work.