What can i do to fix a fan that has stopped working in the heater/ac unit?

What is your question?

One day it was working fine and the next morning when i turned the vehicle on, I also turned on the heater to the defrost setting but it did not urn on. I turned it off and back on. the n I turned off the vehicle, turned it back on but no luck. It does not turn on at all. The lights on it work but just the fan doesn't. Can it be a fuse? Or what may need to be replaced?