Member Avatar for 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

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  • Latest Post Latest Post by comlor

Dani AI

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This looks like a classic “soft‑power latch” problem: the motherboard or its standby circuitry is not responding to the power-on signal unless you fully remove AC or switch the PSU mains off. That narrows the likely causes to three groups — the front‑panel/switch wiring, the board’s standby controller/VRM area (including caps), or the PSU’s standby/PS_ON signalling — so focus tests on isolating those. As pointed out, rule out external power gear (UPS/power strip) early; and as suggested, swapping the original CPU remains a useful compatibility check.

Try these steps in order (safe/non-invasive first):

  1. Disconnect the case power switch from the motherboard header. Momentarily short the two PWR pins on the header with a screwdriver/jumper to simulate the button. If the board always starts when you short the pins, the case switch/wiring is the culprit.
  2. Plug the PC straight into a wall outlet (bypass UPS/strip) just to be sure.
  3. Clear CMOS properly: remove the coin cell for several minutes (not just a BIOS menu reset), then re‑try.
  4. Bench test: move the board out of the case, run with CPU, one stick RAM and PSU only. This rules out case shorts or front-panel wiring.
  5. Visually inspect capacitors and VRM area for bulging, leaking, scorch marks. Bad caps or VRMs can allow the system to only start after a full power drain.
  6. If comfortable with measurements: with PSU plugged in but “off” to the system, check 5VSB (purple) is ~5V and that the green PS_ON line goes low when you press the button. That separates PSU standby from motherboard signalling.
  7. If the symptom began after the CPU swap, try the old processor (or reseat and inspect CPU pins) — a mismatched voltage/VRM load can trigger latch behavior.
  8. If none of the above isolates it, the board’s standby/supervisory circuitry is the likely failure and board replacement or professional repair is the pragmatic next step.

Safety note: unplug mains before moving components and, if you measure voltages, take standard precautions or ask a shop to test PS_ON/5VSB for you.

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Member Avatar for 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.

Member Avatar for 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

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