Pc fans keep spinning after shutdown

fanmotherboardpower supply

I recently build a new system with the following specs:

CPU: i7-7700, PSU: evga 550 g3, MB: msi-z270-a-pro, RAM: cosair vengeance 4×4 gb, SSD: Intel 600p m2
, (no graphics card at the moment)

The problem:
Whenever I turn on the PSU by using the on/off switch on the back of the PSU, the CPU-fan and the rest of the case-coolers starts to spin. At the same time the CPU debug-led on my motherboard lights up (notice there are four debug-leds – CPU, dram, VGA and boot – and only the CPU-light is on).

Details: I can perfectly fine boot into windows by using the case on/off switch, but when I turn off the PC, the fans keep spinning and the debug-led lights up again (the debug-led on the motherboard turns off, when I turn on the PC). The only way I can make the fans stop spinning is by turning off the PSU, thus removing the power.
The PC recognizes both the ram and the CPU.

What I have tried so far:

  • I have tried running my system with an older PSU (corsair 700w gs). When I do this, everything is running fine – the fans stop spinning, when I turn off my PC. Also the CPU debug-led is off.
  • I have tried using the new PSU on an older system with an Asus P8Z68-V motherboard. Everything works fine and there are no problems.
  • No pins on the CPU socket are broken.
  • I have checked that all connections are properly connected – especially the front case-connectors, including the case-switch.
  • I have updated bios and all drivers (even though it seems like it is not a software problem)
  • (i do not have a case speaker at the moment, so I can’t hear any beeps, but i am looking to get one as soon as possibly)
  • I have tested the ram sticks and there does not seem to be a problem with the ram – also, the PC boots fine.
  • I have tried various settings in the bios.
  • I have tried resetting the CMOS.
  • Problem persists when I try to shut down in safe mode.

I think it is very weird, as both the PSU and the motherboard functions fine in other setups. Based on my testing it seems like the motherboard (msi-z270-a-pro) or the power supply (evga g3 550) are causing the problem.

Does anyone know a solution to this problem?
Does anyone know how I can further test my system and figure out what part is malfunctioning?

Best Answer

I finally solved the problem by returning the motherboard to the supplier and buying a new.

This worked in my specific case, but should probably be a last resort for others experiencing the same problem. I also tried to replace the PSU and buy a new one of the exact same brand and model, but the problem persisted, which led me to return the motherboard. If others are experiencing the same problem, there is a possibility it is because of a faulty motherboard, but this case does not provide enough evidence to make a conclusion. One could probably experience the same problem as a result of some other fault. Despite that, I want this answer to be shown, as it might help others with the exact same problem and symptoms as me. Thus if you are experiencing the same problem as me it would probably be wise to at least go through the points under 'What I have tried so far' in the original post, before returning your motherboard.