engine turns over but will not start on 1999 Audi A6 Quattro

I have replaced the spark plugs, fuel filter, battery, but the engine will not start. It turns over and tries to start, but will not.

3 answers
push gas pedal full to floor and turn-over - keep turning over until it starts, might take a few seconds. I know, it feels counter-intuitive, but this works, and was recommended by my garage.
could be fuel pump...easy quick fix....use can of starter fluid in hose under the hood.
check fuel pressure, spark at the plugs, cam timing and compression.