What causes a car not to start after doing engine overhaul?

Hallo I have a an Audi A4 1.9 tdi. I did an overhaul on
the coz it damaged some pistons and the head so I
replaced them together with the bearings on the
crank, rings , clutch kit, the flywheel was
reconditioned. Since then up to now it doesn't want to
start, the computer box was changed also bcoz the
old one was damaged so now don't know what is
happening. Its not starting so its just producing a
sound lyk its want to start. What else should I look at
and to just verify if I have done timing on the fly wheel
correctly.