Macbook keeps turing on from sleep?

Ok this problem is VERY annoying. I usually like to put my macbook to sleep when I go to sleep. So when I wake up I can just flip the screen up and the system turns on. However recently my macbook will just wake up from sleep. I can tell because I can hear the disk drive clicking and checking itself. It will then go back sleep and will do it again. It will do this ever 15-20 sec. If I leave closed enough and open my macbook back up the keyboard will not work, I think this is cause by an overheating. This makes me really mad and its annoying so if you know how to fix this problem that would be appreciated! Thanks