When stuff like that happens (definitely sounds like a virus..), the first thing to try is to boot the pc up in safe mode. You have to hit F8 at the right time when booting up (this link may help: http://www.pcdoctor-guide.com/wordpress/?page_id=624). What safemode does is load the operating system up with the bare minimal stuff, so chances are it won't load up the virus.. Then when the computers running you should run a virus scan/anti-rootkit and get rid of it that way.