It most certainly will be something very simple.
The problem may be an intermittent fault, which behaves itself when you test it, but not when you go to start it.
In that case it's probably a shitty wiring connection, that make connection when you disturb it, but breaks down when sitting normally. A crap HT lead can do this.
Has it had a PScan diagnosis?
I understand if you've had enough but Instead of banging it out to the scrappy, do as Not a number has suggested and offer it for sale as is.
Put a price on it and who knows one of the members here might take it on.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"