There is usually a 125V, 20 AMP line fuse inside the microwave. Its usually mounted at the point where the power cord enters the back of the unit. Unfortunately, you will need to uninstall the oven (if this is an over the range model), UNPLUG it and remove the exterior case to access. The case comes off in various ways depending on manufacture and model. I found this illustration at pcappliancerepair.com based on the model number you listed this question under:http://pcappliancerepair.com/model-display.php
The line fuse is listed as item 28 in the drawing. Keep in mind, there are also a couple of thermostats listed that may also cause no power problems if blown.
One is listed as item 29 (part number 8183703) under the same drawing. The other is listed under the "Airflow" section as item 5 (part number 8183697). The humdity sensor can also be a source of problems when it becomes old. If you managed to overheat the oven any time recently, you may want to check these thermostats and sensors to see if they are still good. They should read 0 ohms when measured out of the circuit.
If the line fuse is blown, you can usually purchase a box of fuses at a hardware store for just a little more than what the manufacturer charges for a single fuse. 125V, 20AMP Ceramic Slow Blow fuses are recommended. If you wish to order on line, use the part numbers to search by comparison as the model number you listed this question under may not be available at all the websites I have provided. The parts, however, ARE listed.
If you have any questions, or need additional assistance troubleshooting, please post back and let me know. I hope you find this information helpful.
NOTE: Make sure you take any resistance readings with the microwave UNPLUGGED and the component under test isolated (removed) from the circuit. These ovens can blow a fuse by simply sitting idle. This can occur from any power fluctuations, brown outs, voltage spikes, etc. Or, it could be the symptom of a component that may have failed. If you find the internal fuse blown and replace it, only to have it blow again, you have a more significant problem than a simple blown fuse.