You need to try a known good PSU (power supply unit) this is an old system so you
will need to make sure you get a compatible replacement, use the specs available @http://www.atxpowers...-atx-300-gu.php
for guidance, pay particular attention to the actual
size of the PSU 6" X 3.5" X 5.5" do not purchase from there as you can get a better
quality one for less, an example can be seen @ http://www.newegg.co...N82E16817371003
Do not power up again with the present PSU as it could blow the whole system, it may
have already damaged some or all other components so loaning rather than purchasing
a replacement PSU if at all possible is my suggestion.
I can unplug a 4 wire connector (2 yellow and 2 black wires) from the motherboard and the power supply light will stay lit when I press the power button, but the computer does not come on.
This is the 12V ATX supply which powers the CPU.