My Frigiddiaire microve (Model # GLMV168KS4) sounds normal and everything else works EXCEPT is not heating up food at all. Please help!!! What parts or part do I need to replace. It's been unpluged for several weeks. I've checked other websites that have suggested what may be the problem and part thatt need to be replaced BUT I want to be sure.

If the light in the cabin lights up and the plate rotates it indicates that the fuse is intact.
That only leaves the magnetron circuit to be checked. The magnetron is a device which generates microwave radiation for heating. It has has three parts :- 1) A heavy duty transformer 2) A high voltage rectifier and capacitor 3) and the magnetron.
The transformer seldom fails , and if the rectifier shorts ( which usually is at fault ) you will hear a loud buzzing sound when you switch on the microwave to heat.Since you did not complain of any buzz that leaves only the magnetron or a fuse before the transformer.The fuse would be typically of 8 to 10 Ampere rating.