I just finished building my new computer.
Motherboard is ASUS Sabertooth Z77
CPU is Intel Core i7-3770K Ivy Bridge 3.5GHz
So I booted my computer and there was this message that popped on my Desktop : Warning, CPU Fan 0 RPM
I looked in the Case, and indeed, the CPU Fan was not running. It looked to be TRYING to run, tho... It was spinning a very little bit (like, half a full spin) and then stopped... And so on.
I turned off the computer immediatly, openened the case and plugged the fan in the Optionnal CPU FAN port. When I booted, I had the CPU Fan Error (of course, since it was not connected in the primary slot anymore). I went into BIOS and like 2-3 seconds later, the CPU Fan started running...
I tried to reboot, and then the CPU Fan started running only when the computer had booted completely (when my desktop appeared)
After another reboot, it started to spin while booting, but not right after I pushed the power button
Another reboot : Didn't start to spin until desktop gave me 2 Warning messages "CPU Fan 0 RPM"
It seems to be pretty random... Could it be the fan ? or the Power Supply ? Or the Motherboard ?