2002 Buick acting up again ??

Last Monday I parked my car only to find the next morning, it wouldn't start. It turns over and has spark but won't fire. This has happened 4 times now. After sitting for a day or 3 it finally starts. I've recently
changed plugs, wires, fuel filter and had the "plate the coil packs sit on" checked and also had the fuel pressure checked. It started Thursday and has been running fine ever since. Fuel pressure was at 42psi. The only code in Catalyst Emessions Bank #1 or P0420 :runaround::runaround::runaround:
I can't see how this code has anything to do with the car not starting ??Anyone have any other help, I would greatly appreciate it. Thanks

Rob

Will it start spraying starting fluid into the intake, do you have injector pulse? A blocked cat could cause a no start but very rare in this car.