I restarted my computer from the windows xp desktop. I noticed the machine make the sound it does when it shuts down. When I tried to turn it back on it would initiate boot but automatically restart after 3-4 seconds.
I tried unplugging and replugging internal power cables to no avail.
I have noticed though that when i disconnect the ATX_12V the system runs but the disk drives do not ppower-up. I guess that the poer supply is initating protection due to short circuit or over-current/under voltage. However I have thoroughly checked inside the chassis and can't find any such problem and overcurrent/undervoltage wouldn't make sense wince I was just using the machine no problem.
Does anyone know the circuitry of motherboards well enough to let me know what to check for issues that might run off the ATX_12V connection. If I connect this while it is running there is a spark and the machine restarts. I cannot access bios at all. This is really bugging me. Any help will be greatly appreciated.
I have noticed though that when i disconnect the ATX_12V the system runs but the disk drives do not ppower-up. I guess that the poer supply is initating protection due to short circuit or over-current/under voltage.
No. The drives do not power up because with the ATX-12 cable disconnected, the CPU doesn't work. You have nothing telling the drives to turn on.
Try to borrow a known good PSU of similar capacity. Or better yet, see if you can test your PSU in another working system. If you cannot do that, try to borrow a DMM to measure the voltages. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.
You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer.