I will be happy to help you out. Can I get the model number to your machine?
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You more than likely have a defective magnetron on your microwave. When everything else works and the only thing that doesn't is the heat, this is most of the time the mag tube. The mag tubes for the microwaves are usually covered by a manufactures warranty for five years, some ten. Check your manual for the details on the length of the extended warranty. Being that you just bought the microwave less than a week ago, the dealer should have an exchange policy through the manufacture. This is not a repair that I would recommend doing yourself if the machine was out of warranty. The prices of some mag tubes can be around 150 dollars or so.
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