No air comes out of vents

What is your question?

When I turn the fan on for the vents no air comes out. It doesn't matter what speed or whether it is the heater or a/c. It started a few months back where it would work and then it doesn't work for a while then it works again. It has been doing that off and on the last few months and now I think it might be totally gone. I am not sure what the problem could be.