It seems like you have one of those viruses that try to make you buy their 'AV' to sort your PC. You'd want to download Spybot S&D and Malwarebytes Anti Malware. Failing that, since you're seemingly dual booting, simply transfer your files onto a CD or Flash Drive. Obviously give them a full virus scan before using them, and simply install XP again. 
Hope you get it sorted
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Hope you get it sorted