Hard drives failing when DVD drive connected

I need some help here. My PC, which I've recently tried to update by adding a 80gb hard drive to compensate for /t killing my hard drive space, won't work. The usual setup of my PC has been one master, one slave on the Primary IDE, and the DVD burner set to master on the Secondary IDE.

When I try to set the 3rd hard drive as slave, or as master, while changing the DVD burner to master/slave as required, the PC never gets past BIOS as it always fails to detect any one of the hard drives. And now, my PC refuses to work with more than two drives! Does the problem lie with my 350W power supply, motherboard, or the hard drives themselves?

Alright, thanks. Guess the PSU is acting up. But, it acted up again a while ago, and this time, while the POST screen was loading and auto-detecting the hard drives, it just suddenly went blank then booted normally. Yikes...might be a mobo problem too...

Anyway, can you recommend a good PSU that's definitely proven to be reliable? Preferrably less than $50.