If you're positive the the microwave caused the problem, then it may have just gone bad. Just like a breaker in your panel they wear out/become weak with repeated tripping.
The curious thing about a GFCI outlet is that it is there to prevent ground faults. First check the main panel to make sure you have voltage across ALL breakers. If not then turn on the breaker that tripped otherwise make sure you turn the breaker off then pull the plug out and replace it.