CPU and 1 of 2 case fans spin for about half a second then stop after turning on my pc

[kamayor41]

I just built my new pc. About yesterday. Turned it on and got it running. I checked up on everything and all the fans were spinning perfectly. About 10 minutes later I looked back and two of them had stopped. Now every time I try to turn it on they spin for a second then stop. I don’t know what I can do to fix it

 

[Paperdoc]

What you describe sounds somewhat like this. The CPU_FAN header on many mobos pays special attention to whether or not the fan on the CPU chip actually is turning and cooing it. It does this by monitoring the fan speed signal sent from that fan back to the CPU_FAN header on its Pin #3. In addition, the mobo monitors the CPU internal temperature (which is measured by a sensor inside the CPU and fed out on one of its pins). If the fan does not turn (that is, the mobo gets no speed signal on the CPU_FAN header), many will give out a short warning and then shut down completely before waiting for the CPU to overheat. Or, if the CPU does overheat after warming up from a "cold start", the system will shut down, too, In either case, what may happen on the next start-up, even if it has bee off long enough to cool down, is that it may refuse to start up because there is a known failure of CPU cooling. This is especially likely if the CPU fan speed signal is NOT detected immediately at start-up.

So, check carefully the fan connections in your system.
(a) Where are they all plugged in?
(b) Is there any fan plugged into the CPU_FAN header?
(c) Is the real CPU fan the one plugged into the CPU_FAN header?
(d) Check that connection to make sure it is secure. Maybe unplug it and re-connect it a couple of times to be sure.

If none of that helps, there's a completely different thing to examine about the way that mobo stand-offs were mounted in the case before you installed the mobo. If there is a problem there it can create a short circuit from mobo bottom traces to case ground, which may only have happened shortly after the first start-up as parts vibrated into place. A short from that source can produce virtually the same symptoms - things start up for only a second or less, then fail. So if fan checking does not help, post back here for more details of this second idea.

 

[kamayor41]

I was actually able to figure it out. I went off some of the stuff you went off. Fiddled with some cords. Got them both working. Thank you

 

[Paperdoc]

Great, thanks for letting us know it is working now.