You can download the online parts List and service diagrams for your model at the following link:http://www.appliancepartspros.com/
To view the service diagrams just use your mouse to click on the link, which is the underlined and highlighted text just above. This will open a new web browser page automatically for you and allow you to view the information at the website indicated. Then just enter the model number of your microwave oven.
You may need ADOBE READER installed on your computer to read PDF documents like the diagrams.
You can download this free at WWW.ADOBE.COM
Click on the DOWNLOAD ADOBE READER button on right side of the ADOBE home page when you get there, then follow the onscreen instructions to install the software on your computer.
I will assume you have checked the house's main circuit panel for any tripped breakers and tested the electrical wall outlet for a good power supply. Reset the house circuit breaker at the panel if necessary.
Otherwise, hopefully the problem is just a blown main fuse inside the microwave. In order to access and check this you will have to disconnect the power cord and then remove the oven from the wall if it is an overhead model. Then remove the case in order to access the electrical parts inside.
Components inside the microwave like the main capacitor can remain EXTREMELY dangerous even after the power cord is disconnected. So if you are not familiar with basic electrical safety precautions when working with this type of equipment, then you should leave this kind of task for a trained appliance technician.
Here is a picture of a generic main fuse for a microwave:http://www.appliancepartspros.com/part_details.aspx?part_id=4440371
Just replace the fuse with an exact match and reassemble. If you tested the old fuse and it was still good, then you may be dealing with a more complicated and expensive fix possibly involving the control panel circuit board. At that point you may want to consider seeking additional assistance or just getting a new oven.
Thank you very much and good luck.