MY SONS COMPUTER WONT START UP

Hello,
My sons computer wont start. A blue screen comes up and then it keeps restarting. I know he was downloading things but would seem like he has downloaded a virus. We cant get onto safe mode to reboot it and we cant reinstall windows xp as it wont connect to the external hard drive. The computer is an eee pc notebook please help me someone as my son is lost without his laptop. Where not fussed if all his details and saved things go missing. THANKS