Samsung over the range microwave oven model# SMK9175ST the microwave part stopped heating

If everything still works, and you're handy with small appliance repair, this could range anywhere from a simple to complex repair.
Using a repair service these days normally costs more than it is worth.

You can purchase a brand new microwave with warranty here: Whirlpool 1 7 cu ft Over the Range Microwave and Speed Cook Stainless...

I hope this helps.

If "everything" works and your microwave just stopped heating, the problem might be with the internal door switches, the high voltage circuitry, or the circuit board or quite probalby your magnetron is dead. If you don't have the technical knowledge to repair microwaves, you should take it to a repair service for diagnostics.