99 Pontiac grand am won't start

In need of help. We have a 99 Pontiac Grand Am SE 2.4 liter the car was not getting enough power while driving down the road from work and was only going up to about 12 to 1400 RPMs after losing power pulled over on side the road and shut the car off but now the car will not start back. We have tested it with a code reader and we get po300. With this misfire code we have changed just about everything possible. We started with the throttle positioning sensor and nothing. we change the camshaft sensor and nothing. we change the crankshaft sensor and then nothing. We also change the coil pack, spark plugs, and fuel filter. While changing the fuel filter we check to see if the fuel pump have pressure and it did. We also had the ECM tested for different times and it was good so we did not change it. We have check the relays and fuses and they all work. The fuel pressure regulator is good. We even reset the system lockout and still have nothing this is something we read and one of the forms that could have been a problem with Pontiacs. We are literally to our wits in and cannot figure this out the car will start to turn over but it will not crank and when we try to turn the key a second time it'll do the same thing but much worse than the first. Does anyone have any idea why the car will not crank

The fuel pressure will have to be checked for a minimum of 44 PSI with key on/engine off. There may not be a Schrader valve in the fuel line so an adapter will have to be installed at a convenient point, usually near the filter.

Another possibility is the timing belt, but checking the fuel pressure (with a gauge) should be done first.

Blue, this has a timing chain.......

I would spray carb cleaner into the intake while cranking to see if it will start....if it starts, it's a fuel delivery problem.......either the pump, or the injectors are not firing(usually a SECURITY problem)....

If it doesn't start, then you have to check for spark......which is not easy if you don't have the right setup to do this.....

More often than not, the problem is the coil tower......that is the plastic tower that the coils sit in.......they suffer from carbon tracking and short out internally.....