Power supply question

My 2.8Ghz system stated to crash. From the way it behaved I suspected power
supply or motherboard; once it crashed on me while trying to configure BIOS.
CPU fan runs fine while powered up.

When I replaced power supply, PC became stable and worked. But it crashed
again after 4 hours or so.

Can a short on motherboard cause power supply to go bad?

I need to see if my power supply is good or not. There are label on the
power supply on voltage; +5V/27A, +12V/10A, -5V/0.5A, -12V/0.8A, +3.3V/24A,
and +5VSB/2A total 350W. The power supply that goes to HD, CD, floppy all
have one red, two black, and one yellow wire. Which voltage corresponds to
different color? Fan power has two yellow and two black. The power supply
socket to the MB has number of Orange, Red, and Black wires with the
addition of white, blue and green ones. What voltage do I need to see on
each line?

Emilio