|You may be looking at some kind of hardware problem rather than a virus. It sounds as if your CPU could be overheating. If you cant get into windows then you could try a DOS based virus checker and a boot disk but honestly I would just reinstall windows, because all you need for it is an XP install disc and you wont need another PC.|
Just choose a different folder when prompted so as not to overwrite your old installation.
If reinstalling windows doesnt work then it is almost certainly a hardware problem, most likeley HDD or CPU.