The pc still had service pack 1 installed. I started to have a problems with explore so I tried to upgrade . I shut the pc down and now I can't get into windows. I have tried safe mode but after the windows logo the pc shuts down. Its not a virus because I have norton security installed . I have tried everything to boot into windows, even reinstalling the disc but the pc shuts down before it will register. I have changed the cd rom in bios to first boot but this has no effect.