Originally Posted by JamesMW
The case fans draw power directly from the psu so I assume its not motherboard related.
The psu gets told to turn on from the mobo, so if the mobo doesnt work, the psu wont be turned on and the fans will never get power.
To test your powersupply, unplug it from all your computer components.
Switch the back of the power supply off, you may also unplug it from the wall at this point.
Take a paper clip, and put it in the pin with the green wire, and the other end into any pin with a black wire. See ATX power supply connector pinout and wiring @ pinouts.ru
Now plug back in the power supply, and switch the back of the power supply on. The fan of the psu should start to spin.
This will tell you if the psu is completely dead or not.
Be sure to turn off the powersupply before removing the paper clip.