1. Unplug the microwave oven from the power and then remove the moving parts from microwave oven.
2. Open the top cover by unscrewing the screws on the right, back and left side using a screw driver. Then you can remover the cover now.
3. Discharge the microwave oven capacitor safely before you start repairing.
4. Check the fuse first if its okay or blown. if blown, replace the fuse with a new good fuse. Test the microwave to see whether its working now. if not working proceed with the next step.
5. check the door-lock switches.If bad, replace the with new ones, then test the microwave again. Remember to discharge the capacitor after every testing procedure.
6. Next step is to check the magnetron whether it is okay or blown. If blown replace it and test the microwave again.