My A1200's keyboard has a loose connector (a tower keyboard adaptor). Whenever the keyboard loses power for even a fraction of a second it will short and give `````````````````.... Longer, and the caps lock will just flash and the keyboard will refuse to do anything - until I unplug it and replug it, sometimes with a power off needed.
You must have a wobbly connector in there. Secure it and the problem should go away.
