If the attic fan or whole-house fan doesn't work, the first thing to do is check if it's receiving electrical power from its switch and from the circuit breaker or fuse box. If you suspect that the motor has burned down or stopped working, you can try shutting off the power and replacing the fan motor. It shouldn't involve any electrical wiring, since most fan motors simply plug into a container inside the housing. If it still doesn't work, the problem is in the switch, the wiring or the fixture, and you should call an electrician. Good luck!