Member Avatar for MattRix

My computer was working fine until tonight. I was sitting watching a movie on TV, and all of a sudden my computer just shut off. I tried to turn it back on, but I got nothing except that my optical USB mouse was still on. None of the fans in the computer turn on, and the power light doesn't turn on: only the USB stuff, that's it AFAIK.

I'm guessing/hoping it's the power supply, any thoughts? Any advice or ideas would be greatly appreciated!

-Matt Rix

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  • Latest Post Latest Post by shahhelan

Dani AI

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Seeing USB power while the rest of the system is dead is a classic ATX clue: the +5VSB (standby) rail is still alive, but the main rails are not starting. That fits what describes and also why suspects the PSU or board. In plain terms, either the PSU cannot bring up 12V/5V/3.3V under load, or the motherboard is not asserting the PS_ON signal to tell the PSU to start. A shorted device, bad front-panel power switch, or an internal PSU protection trip can produce the same symptom.

Try a quick, safe, minimal-power-up workflow:

  • Unplug AC, hold the case power button 15 seconds to discharge, then reseat the 24‑pin ATX and 4/8‑pin CPU power leads. Check for a stray standoff/screw under the board and any burnt smell at the PSU connector.
  • Bypass the case switch: momentarily short the PWR_SW pins on the motherboard header with a flathead screwdriver. If it starts, the case button or its cable is bad.
  • Boot bare-minimum: motherboard on cardboard, CPU with cooler, one RAM stick, onboard graphics if available. Disconnect drives, GPU, and front USB/audio to rule out a short.
  • If it still does nothing, test with a known-good PSU. Alternatively, if you are comfortable and the PSU is out of the case, you can briefly jump the PSU by bridging the green PS_ON wire to any black ground on the 24‑pin to see if the PSU and its fan spin; stop if there are odd noises or smells. Replace the PSU if it cannot run a small load (e.g., a case fan) cleanly.

For : if the PC boots but only the CPU fan runs, check whether your PSU has a zero‑RPM fan mode, verify case fans are on powered headers or a fan controller, and test a case fan directly on a Molex/SATA adapter. If the PSU fan never spins under heat or load, replace the PSU.

Member Avatar for MattRix

Anyone got any ideas, tips, things to check? Anything?

Member Avatar for lornranger

Your PSU (Power Supply Unit) could be blown. Change that. Next on the list would be a dead mobo, but that doesn't make the fan dead. So, PSU is the most suspicious cause.

Member Avatar for MattRix

Thanks! :) Would it make sense that the USB stuff still works though, if the power supply is dead?

Member Avatar for lornranger

I'm not too sure about that. By rights, your optical mouse laser should not be on immediately when you switch on the PC. Thus, if your PSU is blown, I'm afraid that your motherboard might be gone too (something might have shorted, causing supply to the USB immediately). What brand is your PSU?

Member Avatar for nolangwhite

I'm have the same problem. My power supply works but power supply fan and the 4 case fans are not working, also case fan LEDs don't work. Everything appears to be working fine all subs and hard drive get power and are recognized. The only fan that is running is the one on the mother board over the processor chip. All connections appear to be connected. Any help would be greatly appricated.

Member Avatar for shahhelan

Yes when pc is turn on at that time Usb is getting power from pc.

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