fan stopped working, what might cause this

...for your radiator fan, which is what i assume your talking about, aside from the fan, which needs to be tested as well, there is also a radiator fan relay, and a temperature sensor that tells the computer when to turn on the fan, then of course, there's the wiring going to and from everything, and the computer itself..... i had a car where the computer was bad, at least for that function, and wouldn't send the "turn on" signal/voltage to the relay.....

You can check voltage coming from the electrical unit connected to the motor of the radiator fan using voltmeter. See if power still getting to motor. Motor could have gone bad on the fan itself. Check this video out on how to replace. https://www.youtube.com/watch?v=p-MVDWxBY5U

Is it an expensive fix?