Microwave heats food, but cooling fan and turntable do not go on.

My microwave heats food but the cooling fan (not the vent fan) and turntable do not go on. It makes a quite hum and the food heats. Everything else works; vent fan, display, surface light, etc. Funny thing is a few weeks ago the cooling fan would not shut off after food was heated and would just come on by itself. A tap under the key pad would shut it off. Could these two issues be related? What part(s) do I need to fix? Thanks