Jess wrote:
Why would the below be happening?

1. 12 year old over the range microwave stopped working - no power.
2. Microwave on its own dedicated 20 amp circuit.
3. No other outlets or devices on this circuit.
4. The circuit breaker was NOT tripped.
5. Reset the breaker several times (off-on-off). Power restored to the
microwave (enough to display the clock), but as soon as you try to
cook something the microwave looses power and the circuit panel
breaker is NOT tripped.
6. Assumed the microwave was bad and bought a new one.
7. Exact same problem with the new microwave.
8. Recycled the breaker several times to get power to the microwave
again (so the clock displays), but did not try to cook anything.
Unplugged microwave and plugged in a hair dryer. Tryed to run the hair
dryer - no power and circuit breaker NOT tripped.
9. Microwave works perfectly when plugged into another circuit.
10. Assumed the circuit breaker itself was defective.
11. Replaced the circuit breaker with a new one and still have the
exact same problem.

So now logically, it seems that the only problem it could be is
something with the wiring itself. This circuit has worked without
problem for the last 12 years.

Could someone provide some guesses as to what the problem might be?

Possibly a fault with a splice somewhere. Shut off power to the outlet,
test it with a meter (to make damn sure it's dead), remove the
faceplate/outlet, then undo/inspect/redo the wirenut splices inside of the
junction box.

The symptoms do sound a lot like when a breaker goes bad, though.

Jon