Run the disc when you first boot. Wipe the entire HD, and just go fresh install. Simplest way to fix things.XP Media Center Edition 2005 Operating System Disc
That is what it says, I am not sure if it is just the recovery disc or both. Cannot check, as I am at work.
I'm sure it could probably be fixed otherways, but hard to do by someone who can't actually work with it. You might consider taking it to someone to fix it.