There was a huge pop now it won't microwave anything...it runs but no heat or cooking.

It sounds like the magnetron may have either failed or is not being supplied with the extremely high voltage required to run it.

YOUR SAFETY IS PARAMOUNT

This is a job for a professional but if you are safety clued up, here's instruction.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 or moving coil meter on high resistance range for short circuit, (DVM's won't show the fault!), the capacitor can fail and go short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.

Load test.

A simple safety test.
Place 1/2 litre of water in a glass container. Measure the temperature of the water.
Place in microwave and heat on full power for 1minute.
Measure the temperature after it has stood for 1minute.
If the temperature difference is more than 9 degrees Celcuis the magnetron is working and producing about 700Watts of heat.
If your microwave is labelled with 900 or 1000Watts. That is about right.
If the temperature is less then the magnetron is not working properly and may need replacing.

This a only a rough guide and any doubts you should consult an authorised service agent.