help my 2001 alero wont start

My car will not fire. ive been fighting with a hard starting and a stalling car. ive changed the spark plugs and wires, cleaned injectors and replaced the Idle Air Control plus GM dealer had car on diagnosis computer for over 3 hrs and no codes. After i changed IAC it worked great for 2 days and then car sat for 2 weeks now problems have gotten worse and today it wont even fire up.it spins over but no fire.

Have you checked for spark at the spark plugs? You could have a problem with the 24X crank position sensor.

Assuming you have a 3.4L engine, also check the fuel pressure at the rear fuel injector rail Schrader valve to see if it is in specs.