I'd just replace the mainboard. I know he said he isn't a technician. Maybe have a buddy that is a little more techy do it. It is really unplug unscrew, screw, plug in. See if they will ship you a new mainboard. The steppers rarely go out. Cables go out and can possibly short and fry the board. Bad thing is if you replace the mainboard and a cable is bad, it will short the new board also. I would replace the x stepper cable, it is the only one that bends constantly and the switch cable too. Inspect all the thermocouples for shorts or breaks in the wires.

Also this is big, check for any heat related issues/discoloration on any of the plugs. How the wires are tinned and then inserted into the plugs is bad and can cause bad connections. The main power plug going to the board and the Build plate heaters are the usual suspects because of the power they provide.