Do you get any lights on the dash?
Is there an imobiliser?
The 'isolator' describe?
Is it 'by-passed' with a bit of wire with an inline fuse by any chance?
If the dash lights up, then you are looking at an inhibitor somewhere, possibly an imobiliser, or tyhe fuel pump safety cut-out.
Imobilisers are a pain.......
But of there's an isolator, common to by pass with a low amp fuse to allow small current to the clock and raio etc to keep time and momory functions alive, but any greater current draw, like trying to start the engine will melt the fuse and stop the car being nicked.... (in theory!)