About a year ago, I assembled a system with a MSI motherboard and Celeron processor. Initially I installed WinXP Home, and later did dual boot with Suse Linux. It never did boot properly, and I'd have to power off and on several times to get it going. It ran 24/7 connected to internet, and a couple times it had rebooted itself during the night.

Anyway, I wanted the psu for another computer so I installed a new CoolMax 450w psu and then it wouldn't boot. No beep, nothing but a black screen. I put back the old psu and same thing. The battery checked out okay and I cleared the cmos with no luck.

Then I unplugged the case fan which gets power from the main board and she booted first try, same with the new psu which is now installed. I'm guessing that the fan was somehow depriving the motherboard of power.

I would appreciate if anyone could shed some light on this, and also if I could power the fan directly from the psu.

If what you are saying is true, just unplugged the fan and it worked, then I would trash that fan. I wouldn't try to plug into anything else. Unless you somehow plugged into the wrong place or the plug-in on the mobo is bad then I would say the fan is junk. Fan's are cheap-replace the fan. Better safe than sorry.