Sounds like it's time for a new one. They're very inexpensive, though, since you can find them for under $10 apiece. Just go ahead & buy a replacement.
EDIT: Sorry, didn't realize that you were talking about a laptop (thought you meant a desktop keyboard).
Assuming you can get inside the case, clean it out, & then reassemble it....if it still doesn't work, it's probably time for a new laptop. And to be honest, even if it does work after cleaning it, I'd start backing up the data & planning on replacing it anyway.