Good advice from Dinah, Grace.
In the geek world this is known euphemistically as a "Japanese reset."
The ESSENTIAL step is to UNPLUG the device from the wall. Just turning the device off will NOT reset it. You don't have to wait forever- just count to 15 of so before plugging it back in.
This is one of the first steps many technicians take nowadays before they get out the flowcharts and logic diagrams, and it has saved my butt a few times, thereby boosting my ego immeasurably.
That being said, there comes a time to cut your losses and get a new unit. I would go with XP Pro rather than Vista. Vista got a lot of negative press. Perhaps someone can tell us if Vista has come out with Service Pack 1 yet... If they have, I would reconsider. Vista is supposed to be the MS operating system of the immediate future, after all.