Power Mac - Is my power supply dead??

I know there are a lot of topics covering dead power supplies, but here goes my case....

I run Pro Tools on my mac (G4 quicksilver) through a USB powered MBOX and with two firewire 400 drives chained together. At some point it started giving me errors every time I tried to record or playback, saying it couldn't get info from the drive fast enough.

At the same time, I was having issues with intermittently losing power to my USB-powered devices like my mouse, keyboard, and Ipod. All cabling good, ran everything right off the hard drive slots to test. Also, problems playing back audio - not through pro tools itself, but itunes, or DVDs, any sounds through the pro-tools USB audio interface. The audio and video playback would be choppy and hang-up/skip a lot. if I quit the interface program and just played audio through the built-in audio, all is fine.

I suspected that my USB was dying so I bought a new belkin USB 2.0 PCI card. But when I installed this, the panic screen came up and said to restart immediately. When I did, I had lost my firewire drives (wouldn't mount on the desktop.) I restarted, reset PRAM, unplugged everything, plugged back in - everything any forum suggested. When i plug them in, you can hear the drives start whirring, but they never show up on desktop or in system profiler. I went so far as to buy a new Firewire PCI card to see if the original ports were dead - nothing still.

Days later, was on the mac when everything froze with the beach ball of death. Restarted and get a question mark most of the time. If I leave it off for a day and turn it back on, I'll have functionality for 10 minutes before the freeze cycle happens all over again. There is also a high pitched electronic zap noise/beep that occurs.

So, is my power supply dying and causing all these failures??? that's my guess.

Sorry this is so long; wanted to give the forum a shot & tried to be as specific as possible. Hopefully anyone with similar problems might learn something from my problems as well!