I defragged this morning, cleared my cache, I do a daily virus scan (all definitions are up to date) plus a weekly trojan scan which didn't show anything up just now. Ran spybot yesterday - I even went to pcpitstop - apart from being very slightly low on disk space everything was fine there too. I'll try a system restore next - if it doesn't work I really can't think of anything else to do apart from reformat.
