1991 buick regal 3.1 turns over but wont start why?

Timing belt, or chain has jumped timing, if you have fuel, spark, and compression--I had a problem with a 2.8 chevy engine once--and it turned out to be the fuel injection pressure regulator! Had good fuel pump pressure, spark, compression etc. but would not start, fuel injection pressure regulator was bad, and the injectors didn't have the correct pressure to work. Don't know if your engine is fuel injected, but that is something I would check before tying in to the timing belt/chain.