This probably isn't your situation but I had a similar incident happen on a computer of mine a while back. The problem ended up being that I had an old wireless keyboard in a cabinet about 10 feet behind the computer. Because I was still using the wireless mouse I hadn't disconnected the receiver. That drove me crazy for about a week.
Like I said that prolly isn't your problem but it pays to think about things like that. It could be something completely out of the blue.
I tried using safe mode and the repeating character problem stopped but when I re-booted I got system restore re-booting time after time. In the end I did a full a full restore and re-installed everything, including the o/s and everything is ok now.
Many thanks to all for your help and suggestions
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