Dead Shuttle Xpc?

I am a new computer technician for the school that I work for. I've had quite a few problems since I started working but that's off topic. I have a Shuttle Xpc that has a Pentium 4 2.0 Ghz with 512 MB of RAM and a forty gig hard drive but the computer has had trouble turning on ever since it was moved before the school year ended last year. You press the power button and you had to wait for fifteen minutes at least before the thing turned on and it has slowly gotten worse and today it hasn't turned on at all. Is this problem because of power? and if so what is the fix? Just to get another shuttle or to strip down the current shuttle and put in the minimum and go from there. I also opened the Shuttle and felt the power supply and it is extremely warm and the thing hasn't been on all day like I said. I'm not certified but I'm very good at trouble shooting and I'm working at the school because it will look good on a college application because it will show how serious I am about this field. I wasn't the best student and am having trouble getting into college.