Apparently, spybot did find something that supposedly was messing my registry up (no other critical objects or anything else apart from cookies).
Rebooted and it was still a massive pain to make the bloody thing start.
I was, however, able to write all documents and media files onto DVDs, so I guess the worst thing that can now happen is I have to buy a new HDD (well, or PC, but I'd rather not!).
Will try the rootkit revealer to see whether I can sort anything out.