I don't think that swapping PSUs fixed the issue. I believe that it was chance that it worked. Sort of like when you took it your friends house and it worked.
A few months before I started to get in to the IT business I had a computer with nearly identical issues. I tried for days to get it to work. Finally I took it to a computer shop. They plugged it in and booted fine. Luckily they didn't charge me and they sent me on my way saying there was nothing wrong with it. This was my first custom build.
After about a year 2 RAM slots went bad on the board. The board died about 2 months later. I am still using the same computer (kind of). I slowly replaced every
part in the rig, even the case.
The symptoms you are having (minus the inconsistency) I have seen multiple times in machines with faulty RAM modules or bad slots on the board. Again I will stress to try different RAM first. Try one stick and in different slots.
If that fails I would defiantly be leaning towards and issue with the board. The power supply is the last thing I would suspect in this situation. Like I said before PSU issues symptoms are almost always the following:
Press power button
Borrow some RAM from a friend and let me know the results.
Edited by Titan8990, 21 July 2008 - 08:26 PM.