G4 won't boot. No startup chime. Power button light goes off right after I power it on. Fans go on and soon switch to high / fast mode. Tried everything imaginable -- removing all cards, RAM swapping, PMU reset, bought a new 3.6v PMU battery... everything on this forum (I think) except buying a new power supply which I'm trying to avoid. Is that my next step, and if so recommendations on where to buy? Is there a way to confirm it's the PSU before I buy a refurbished one?