Power supply unit problems?

I've been converting car audio systems to home systems and I ran into a problem with the power supply I just got... I yanked it out of an old dell tower and noticed it was packed with dust so I used and air hose and cleaned it off... To operate it I had to jump the green wire to one of the black wires on the motherboard plug.. I've done this befor and never had a problem... But with this one the supply came on for a second then shut off and wouldn't turn back on for about ten minutes and it did the same thing.. I have no clue what's wrong with itt