Humn. When I first read that, I thought those aren't meant as spacers - but I guess the ports line up at the back so they must be. I wonder if one of those big bumps is touching something it shouldn't
Is there an on/off switch on the back of the PSU?
If it were my computer, I would remove everything from the case and setup the just PSU, motherboard, CPU/heatsink, and beeper on a clean cardboard surface (insulating, not too hard, and nobody cares if it gets scratched) ... but bare in mind that I don't have the best record with components and have had smoke poor out of them on occation
As a bonus, having it out of the case gives better view, so you can more easilly check every switch/jumper/connector on the board so you know what they do.