What does it do when you try to power it up? Do you get video at all? Is it the DVD drive that has stopped reading discs?
Actually, to be honest - FiRez' reply is pretty much spot on...
1. If the HDD is dead you won't be able to swap it into a new box anyway, it's dead!
2. If the mobo is dead you're hosed because you can't get the HDD key to get access to the drive.
3. If the DVD drive is dead - why not swap in a new DVD drive instead?