Hi, I acquired (for free) a dell Dimension E510 and it it does boot up. When I power it up, it makes a terrible beeping/whining noise and then powers down. The power indicator light starts to blink and I can't power up the computer again unless I hold the power button down for 10 seconds or I unplug the power and then push the power button again. If I disconnect the square 4 pin connector from the mobo, it does not make the beeping sound and the power indicator light stays solidly lit, Regarding the PSU 4 pin connector, I am getting 11.95 volts on each yellow wire (with a volt meter to the chassis) and (minus) - 2 volts on the black wires.
I have tried removing and replacing the cmos battery, disconnecting the modem card, hard dive. Its only when I unplug the 4-pin connector that the computer does not beep and turn off

What does the 4 pin connector supply power to?
Does it sound like the 4 pin connector is good?
Could the mobo be faulty?

Thanks, Bill