I had to reformat my computer...?

I had to reformat my computer because the blue screen of death kept coming up whenever I tied to turn it on...So I reformated it and then reinstalled Windows XP Software from my CD, but now it keeps telling me that my software isn't authentic and that I may be a victim of counterfeiting...What should I do? I know that I'm not a victim of counterfeiting, it's just that my software wasn't meant to be used more thanonce, but it's not my fault that my computer made me have to reinstall the whole software...What should I do?