Databaseben is correct, maybe. You need to buy a legitimate copy and changed
the license key in your current installation to the new one. Be sure to buy
the same version of windows. I have read on the web that it is possible to
get this error even if you have a real copy if you change more than 1 or two
hardware pieces on your pc at a time. Windows takes an inventory of your
hardware when it is installed so it knows whcih computer it is on - if you
have to install a new hard drive and other componenents as a crash, the hash
it created based on your hardware could change enough to make the legitimate
windows copy think it is not legitimate.
Your best solution is to cal microsoft's number, explain what happened, and
they will tell you what to do. They won't bust you for having a pirated
license key - but will tell you the best way to get it resolved - even if
that means buying a real license key.
Mike