you should start with the button, obviously
Well, first thing first you better wear some protection clothes, like some specials gloves & acarpet isolated electrically (i forgot the specific names of thoses things). Even if you cut the power off, there will be still some power inside capacitor'n shit (i hope you also have a multimeter if you want to work safe).
But for everything else i don't know shit, so good luck with that.
This actually might help.
I have no idea how to fix them though honestly. I am not trained or authorized to do anything at my job but let the power tech into the room with our UPS units.
We also have a 30x50 space with maybe a hundred massive battery jars.
It's heavy duty shit.