Take the machine into a local repair facility and have them test the power supply unless you have a power supply tester.
Also, have them "jump" a known good power supply to the motherboard to verify the board is good. Both tests should take less than 30 minutes and the cost should be minimal.
Also, have them "jump" a known good power supply to the motherboard to verify the board is good. Both tests should take less than 30 minutes and the cost should be minimal.