OK, this is, as you suspect, a main board issue
Turn off the power,
Remove the screws around the door.
The front part of the door will come away, leaving the inner door and all the electricals in place
Look carefully at all the connectors, wiring and components.
You may be lucky and have a bad or loose connection.
If you see burn marks on the main board, its almost certainly not worth repairing as parts are so expensive on this. Also, even though you may not have used this a lot, it will soon be approaching the time when some of these parts will become increasing difficult/impossible to find
Hopefully you will find a loose connection
If you need more help, please just ask.
In the meantime,
Can I ask you to take a moment and rate my responses so far? Please use the smiley faces which you should now see. Please remember you are rating me personally, not the website or the problems you have had with this machine.
This will not close your question and you can still come back to me if you need more help