Keys typing by them selves....

Please help! A while ago my computer started randomly typing the same key over and over, as if I was holding it in. I restarted the laptop and it stopped. A few times after that the same problem happened with different keys, making it impossible to do anything until I restarted the laptop. Now it is happening again with the "5" key and nothing, not even restarting has helped. I've tried various virus scans and although I got rid of a few viruses, the problem still stayed. I tried banging the keyboard as well.
Please help! I'm typing this on my iPod!
Thanks in advance!
John