The first thing I would suggest is to turn off the breaker or unplug it from the wall for a few minutes to "reset" it, then try again. If a reset doesn't fix it, I would think you may have a defective magnetron. When you heat something of very low moisture content, it can lead to microwave energy not being fully absorbed, but instead being reflected back to the magnetron. This can damage it. This is usually best left to a pro to repair. In case it might help, your owner's manual can be found online at: http://products.geappliances.com/ProdContent/Dispatcher?REQUEST=SKUOBJECTS&DOCUMENT=Use%20and%20Care%20Manual&SKU=RVM1425BA
It sounds like the magnetron may have
either failed or is not being supplied with the extremely high
voltage required to run it.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 on high resistance range for short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.
Here is a tip that will help you to figure out what is wrong with your Microwave Oven....
Basic Microwave Oven Troubleshooting Tips
If there is spark please do not switch on unless you have confirmed the fault. It is possible that the Magnetron is leaking and sparking to the ground. It is quite possible that insect can get into the oven and create soft spots. When you switch on these will create a short and make the voltage jump and in the long run damage the magnetron.
So Remove cover after disconnecting , check for dirt/moisture in the cabin, if so wipe clean and dry, check the magnetron and area clean and use an jet air to clean off.
Now keeping clear switch on , use a cup of water inside to test.
If you notice any buring smell shut off as the magnetron or the main HT capacitor can be faulty. replace with same type.
If there is no heating the magnetron/capacitor/temperature cut off is faulty
Usually answered in minutes!