computer will not power-on unless I unplug power cable

[fnukyguy]

After shutting down, my computer will not power-on again unless I unplug the power-cord, then plug it back in (or use the psu on/off switch).

I have tried changing PSU, same thing happens.

My guess it has to be related to my motherboard.
I have the latest bios. I have reset the bios.
This happened after upgrading to a opteron 180 cpu. But I'm not sure if its related.
I have tried disconnecting the RAM, harddrive, graphics card to no avail. Also tried refitting the power-button cables.

Computer is rock stable once its on ...It powers on fine if I switch off the PSU with the button that is located on the psu, or pull out the power-cable before turning it on.

Any ideas what might be causing this?

Epox 9npa+ultra motherboard, amd opteron 180 (939), win xp sp3, 2gb ram

[Kraai]

I'm not sure what a psu is? If you mean the ups (uninterrupted power supply) then it seems that that may be where your problem is. Try to temporary bypass the ups by plugin your pc directly to the power supply, and see if it boots up.

[comlor]

I'm not sure what a psu is? If you mean the ups (uninterrupted power supply) then it seems that that may be where your problem is. Try to temporary bypass the ups by plugin your pc directly to the power supply, and see if it boots up.

Kraai = PSU = Power Supply Unit

Does the same thing happen if you put your old proc in the system. Since the problem started after the upgrade i would try undoing the upgrade to eliminate that as a possibility. Also check the bios setting for your proc to make sure it clocked properly. If you had old one overclocked it will be using the settings in the bios for the old proc