A cheap power supply costs very little...maybe 25 bucks. Pick one up, replace the old one (not as hard as it sounds, but watch that those connectors are hooked up right), and see if it works.

If it works, that was probably your problem.

Now. Take that new cheap power supply out, save it on a shelf for future emergencies, and get a really good one. I recommend this outfit. Depending on what you get, it will cost more (sometimes a lot more) but a quality power supply will pay for itself in trouble-free operation. Like hard drives and RAM, it's one area you don't want to skimp in as far as quality goes.

Figure out how much wattage you need, then get a bigger one. Except for cost issues, and sometimes fitting it into the case, you can't get a power supply too big for your system. It will draw only what it needs, and a power supply that's cruising along at much less than full capacity works better than one that is at its limits.

Obviously, it's just fine to use the cheap supply until the new one shows up.

I plugged in an old machine that had been laying around a while, and the power supply actually exploded. Went BANG. Thought I was going to die. One of the big capacitors had blown. Inspection showed that the ends are scored in such a way that apparently they are designed to let go like that under stress. Who knew?