I have a video workstation I built w a generic 750 w power supply running a core2 quad 9550, w 8gb of hyper x memory and 6 hard drives. recently system has been unstable...like its underpowered and locks up. Once I unplug several hard drives the system becomes stable again...I can plug them back in and the system maybe stable for a few days or a week. then it starts locking up again. I tried to rewire it, which didn't help. I'm thinking I may need more juice. It doesn't seem to matter what drives I unplug, just that I lighten the load....
It's not an issue of having too little power, unless you have a crossfired video card setup you didn't tell us about. 750W is WAY more than enough for that setup with any single video card.
It IS entirely possible that your PSU is on the fritz, though; generic power supplies are trouble, and since I'm guessing this system would be about 3-4 years old, you're right in the danger zone. Definitely need to check that out sooner rather than later if you don't want it to crap out and take other components with it.
Really the thing to do is get out a multimeter and measure the PSU voltages. They should be within +/- 5% if you have a healthy power supply. That means the 12V rail should be showing between 11.4-12.6V, and the 5V rail should be 4.75-5.25V.
There is free software you can get that will attempt to measure the voltages, and I stress "attempt" -- it is nowhere near accurate enough to tell you whether you actually have a problem, so I wouldn't recommend it.