[aliensyndm]

Well there's a few things you can do. If there's another working PC nearby you could always take the hard drive out and hook it up as a slave to the working PC and get any pictures etc you might need from it just to be on the safe side.

Get the hard drive back on the bust PC.
Get a windows XP cd, whack it in and switch it on. If it doesn't boot from this go into BIOS and set it to boot from DVD drive/cd ROM drive first.
You can then try doing a windows repair and see if that sorts it out.

At the moment it's not entirely clear if it's hardware or software related yet.