If the fan is turning, you have all of the knobs in the correct positions and the power on, then it may be the heating element. It's usually a quick and easy fix, but if you've never done it before, get a handyman out for it. Also, if it's a managed rental, it shouldn't cost you anything to get it repaired if you call your letting agency. If it's privately rented, check your tenancy agreement. Some landlords will cover it, some won't.