My over the stove microwave starts continues for a few econds the f-7 appears and it stops

F7 means power to magnetron is interrupted.

I don't recommend that someone without experience and an understanding of the safety procedures undertake troubleshooting this.
You can find manuals and helpful exploded view diagrams for your model here and my favorite parts supplier is here. There is a technical sheet hidden behind the controls that has helpful technical and troubleshooting information. It will say something like this:

F7 Power to magnetron interrupted

1. Unplug microwave oven or disconnect power.
2. After 40 seconds, check to see whether this solves the problem.
3. Unplug microwave oven or disconnect power.
4. Check cooling fan operation
5. Check the magnetron.
6. Check P65 connection on the relay control board.
7. Check the P56/P66 connection between relay board and relay control board.
8. Check wiring to the 1200W inverter and control system. See "Checking Inverters."
9. Check operation of all interlock switches.
10. Replace all parts and panels before operating.
11. Plug in microwave oven or reconnect power.
12. Check voltage at 4903-1 on relay board. If it is 120, unplug microwave oven or disconnect power.
13. Replace inverter.
14. Replace all parts and panels before operating.
15. Plug in microwave oven or reconnect power.
16. If problem persists, unplug microwave oven or disconnect power.
17. Replace relay control board.
18. Replace all parts and panels before operating.
19. Plug in microwave oven or reconnect power.
20. If problem persists, unplug microwave oven or disconnect power.
21. Check for reversed plug connection on controls or loose wiring.
22. Replace all parts and panels before operating.
23. Plug in microwave oven or reconnect power.

William E. Miller, AS-EET
http://www.MicrowaveControl.com
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"