Presuming it has a coil and the 'distributor' on the front of the cam: check for spark. If no spark: check crank position sensors in the bell housing for coil continuity. If they are ok pull off the wire from the ign key to starter and then get a friend to hold the key in the start position (engine will not be cranking). Get under the rear of the car and listen for the one (or poss two fuel) pumps to be running.
Flush the stale petrol (gas) out, replace fuel filter and put 5 gallons in. Then the fun starts....... All the rubber under the bonnet (sorry hood), new battery, check test battery cables, check test alternator, consider tyre replacement - oh the list goes on......................
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i