If the car cranks and cranks and you have changed absolutely nothing at all since the last time I did start, I would be it has something to do with the CPS.
1. Does the tach move or "bump" at all when you crank it? If it doesn't move, then no CPS signal.
2. If it isn't moving, have someone wiggle the harness connector for the CPS and see if that makes any difference. You are working with a potentially 25+ year old harness that will be brittle as heck over there on the exhaust side.
I've seen that happen on many MK3's over the years and if the tach isn't bumping or moving a bit, then something having to do with the CPS is usually to blame.