smc,

Whenever posting questions on these forums, please give us as much information about your computer as possible. We need the operating system, processor speed, amount of RAM install, the age of the computer, and anything else you think might be helpful. The more information you give us, the better informed our answer will be. Enough of that, back to your question.

Have you disconnected the keyboard? Unplug it. Is it possibly a sticky key and removing the keyboard will stop the problem? If disconnecting the keyboard and swapping in a new one fixes it, either clean the keyboard, (which you said you've already done) or get a new one.

Hope this helps.

Grif