I agree with disconnecting the mobo... something on it may have shorted. It draws too much current and the power supply shuts down to protect itself. Note that it's possible that the drives alone may not be enough of a load for the 3000 power supply, and it still won't power up, so you learn nothing. I've seen it on pc supplies, but don't recall ever trying it with a 3000. I used to put dummy loads on the 5v in those cases.
Anyway, check out the serial port level shifters. at U304 and U305. I've seen those fail on a 2000, and short the -12 to +12v & give the same symptom. It's a place to start anyway.
