Strip the wires with your teeth whilst psu is on, if you fly across room and your gums bleed It's got some current.
If you just feel a mild tingling and you get new hairstyle then replace it.
Did that. Just some tingling. Hmmm. But then, it's supposed to output only 12 volts.
Last night my system wouldn't turn off, and I had to unplug it. It's looking like a new power supply may indeed be needed.
I ordered a tester from Circuit City for 16 bucks. I also got a replacement for my 2-year-old, 430W Antec, amazingly cheap at only $24 with rebate.