Microwave runs but doesnt heat

Runs ?? I guess you mean the light comes on and it rotates ??

Make sure its is on high cook mode ( in case someone has it on defrost etc) Try it with a half glass of water - if it does not boil, chances are your microwave unit inside the case has died - not uncommon fault and not worth getting fixed as the replacement part + labor is more than the cost of buying a new one.