Difficult to tell what the problem is with so little information. However, if you revert the machine to a previous restore point Windows is going to continue to try to download and install any updates which were issued after that restore point.
It could be almost anything. Perhaps the machine contains a faulty piece of hardware for which Windows Update is trying to download and install a more recent driver.
How long have you had the machine? If it's still under warranty, I'd certainly take it back, though you got it from PC World so I wouldn't get my hopes up if I were you...