I am trying to fix my old desktop that stopped working this past summer. When it stopped working, I was playing a video game and the computer simply shut off.
Here is what happens now when I try to boot my PC from a powered off state by pressing the power button:
- My CPU fan twitches slightly, but doesn't spin
- All other case fans spin up as normal
- All of the phase LEDs on my motherboard light up and stay on
- My HDDs and disk drives sound like they spin up normally
After this, nothing really happens. My monitor doesn't receive any display, even though it's on, working on my other PC, and I've tried both of my video card's outputs.
The oddest thing is when I go to shut off my PC. When I pull the plug it simply goes dead, but when I hold down the case power button for 3 seconds, this happens first:
- My CPU fan spins up immediately then loses power again and slows to a stop after a second
My first thought was that my CPU fan was dead, but it seems to be working, just not on. I tried connecting it directly to a system fan connection and it spins up and continues spinning without problems.
I have reset the CMOS for my motherboard, and my next step is getting a can of air and resetting all the components in the PC. What could cause this odd CPU fan behavior?
Best Answer
There are only two reasons I can think of:
Unlike the case fans, the CPU fan is completely temperature controlled. I suspect the CPU doesn't generate any heat (i.e., it's dead or it doesn't receive power), so it never reaches the minimum temperature to turn its fan on.
The fan is actually damaged and the computer refuses to turn on to protect the CPU.
Connecting the CPU fan directly to a 12 V outlet (e.g., a spare case fan connector on another motherboard) should let you rule out a damaged fan.