It may be as simple as corrosion in the connectors of the underbonnet fuse box.
If you undo and lift the fuse box then unlatch and replace them all a couple of times it might do the trick.
I've had quite a few non starters over the years with this problem, the most recent last week
While you're in there you could also check continuity between there and the ECU and inspect the wiring for any damage
Russ