Update: The bastards are magnanimous enough to allow a special mode where a browser can be used to go to pay for a genuine liscense, but no way to restore what you already paid for. So not only do they accuse customers of theft, they hold your pc hostage to extort more from legitimate users. I despise them. Do not trust MS with any data you have.
So did you actually have a genuine copy of Windows on your PC? Why did it suddenly stop working, was it due to an upgrade or something?
As an aside, I don't actually think it's unfair for MS to block access to Windows to users who are using illegal copies of Windows. It's their product; it stays their property so long as you haven't pay for it. If you don't like that, use something else instead (like Linux for example) or pay for the license.
Please note I'm not accusing you in particular of using an illegal copy of Windows. I'm just expressing surprise at people getting outraged when their PCs stop booting up into Windows because they have invalid licences (there was a story in China recently, which as I remember it was reported with glee by one of the Mac sites.)
(PS you could always load up the hard disk on another machine and copy the data from there)
I have a valid liscense that came with the OEM HP computer. Still have the receipts. Vista worked for 2 years until last night when it became invalid and accused me of theft.