have you trie removing power to it for a couple minute to see if it will reset?
Either unplug it of flip it's breaker off depending how it is wired in.
I did look up the wiring diagram for this unit and there is a fuse in the magnetron circuit but something would have cause the fuse to blow.
Below are some of the parts that may do this with approximate prices.
Control Board $160.00
Add labor to this and you are getting close to the cost of a new ubnit.
It could be something that is less expensive but it is a gamble.
A microwave is not something that you should tackle unless you have some electrical experience.
The magnetron uses high voltage which is very dangerous and some units do not automatically discharge this voltage when unplugged.