Have a 2000 buick century was running great parked it for the night went to start it the next morning it would not start, put in new fuel pump, fuel relay switch, n fuel filter. still will not start.

If you have a spare key, try changing keys. May be the key fob. Also check fuses.

Before replacing part's testing the fuel system should have been done , fuel pressure an flow an voltage drop testing the electrical circuit . Did you do a engine compression test ? What engine ? 3.1 ,3.4 or 3.8 l V-6 The timing gear an chain on these wear out . Teflon on the cam gear goes . If it has spark an fuel pressure wouldn't suspect the PCM - engine computer. When you turn the key to the run position does the check engine light come on , If it does , would not thing the PCM bad ! Did you check the PCM five volt reference circuit ? A few of the engine sensors use this five volt ref. voltage and if a sensor is shorted it could cause a no start condition . The TPS - throttle position sensor is easy to get at . Three wire's ,the gray wire should have 5 volts with key in run position . The engine coolant sensor , MAP sensor ,A/C pressure sensor ,fuel tank pressure sensor ,EGR valve all have a 5 volt ref. voltage . No five volts on the gray at the TPS would indicate one of these other sensors was shorted . You don't have a SECURITY light lit on the dash ? Anti-theft system problem ,the PCM will not energize the fuel injectors . Try spraying some carb . cleaner into the engine through the throttle plate an see if it starts then .

Depress the gas pedal halfway while cranking. If it starts, that's the symptom of a bad engine coolant temp sensor. Makes computer think engine is warmer than it is and PCM gives too rich or lean a mixture making it not fire up