A fantastic tech post from Brother in The Craft, binthere222:

In my case, I have found the easy solution to the numerous "Dead Advantium" posts I have seen. This seems to occur with amazing frequency, when power is available, but nothing comes on at all. GE sure doesn't make it cheap to fix and it seems that ALOT of excess work is done when all it takes is the replacement of one little item.

It was an easy fix to remove the control panel and then the Thermal cutout fuse shown. Once replaced, All the lights came on and it started to work again, No problem.

The Thermal Cutout Fuse is heated by air exhausted from the cooking chamber of the oven. If there is a food fire or other other overheat condition, this fuse is supposed to temporarily open, Thereby bringing all operation of the oven to a DEAD STOP. Emphasis on the DEAD, i.e. electrically dead. Problem is, these little fuses are poorly designed/constructed such that they will remain open when they are supposed to close as the oven cools off.

UNPLUG THE UNIT FROM HOUSE POWER BEFORE DOING ANYTHING !!!!!

1. There are two screws pointed straight down above the upper grill. Remove those with a phillips screwdriver, then pull the grill off.

2, One stainless screw is now revealed above the center of the control panel. Remove it and then slide the panel up 1/2 inch by pushing/tapping up from the bottom of the control panel then lift it out.

3. There will be less stress on both you and the equipment if you just remove all wiring harness plugs from the rear of the control panel.

4. You will then be able to see the offending cutoff fuse secured by one screw to the floor of the controls cabinet just behind where the control panel sits. Test across the two terminals. If you get no continuity or anything more than ZERO ohms, then replace the part because it is not providing a closed circuit EVEN THOUGH THERE IS NO HEAT CONDITION PRESENT.

5. Remove the two white plastic insulated spade plug connectors, then the one screw and lift the part out.

This Shows the General Location of the Fuse at the bottom center after the control panel is removed

This shows a closer view of the Fuse

This is a view of the aluminum bottom of the fuse

When the fusebottom is removed the mechanism is revealed.

The small purple stick is made of a ceramic or plastic which expands slightly when heated. One end of the stick touches the aluminum, the other end pushes against a flexible brass strip (at the small dimple in the center). This causes two contact points to separate, thereby opening the circuit. The contact points appear to be oxidized from the presence of heat, DUH !!! and dampness from cooking food.

You can buy the replacement thermal cutoff fuse here ==> http://www.repairclinic.com/PartDetail/Thermal-Fuse/WB21X10046/769674

To learn more about your microwave or to order parts, click here.

Source: Dead GE Advantium Microwave Solution, Thermal Cutoff Fuse