There 're 2 methods right now

I just met the same problem, but I 've not solved it yet. First method is to reinstall the whole XP pro but DO NOT accept any security updates. This method is very unsafe that your computer might get other problem and at risk to virus. The other method is just like above people said, spending money for a so-called "genuine" version. Or, you may install other OS, like Mac, linux, but I wouldn't recommend that because then you have to start learning a completely new OS.