Building on Sarma's suggestion, do some board swapping to figure out if it is the power supply or the mainboard you are plugging it into.
Try a different powersupply on your main board. Does it work? Then your load is good and the power supply or cable connector is bad.
Or try the power supply on another main board, if it doesn't work then take the cover off and try to elimnate sections that are still working.
You may find the black resistor,transistor with three legs and no body,etc. Replacing it may not fix your problem. You may have to find out what caused the failure and fix that.
The molex connectors that attach to the motherboard and other components usually only rated for twenty connections or so, so per Sarma, check each of the 5V leads on the motherboard in a convenient location.
Mark