Car won't start

Chevy Impala 2005 V6 3.4liter 95,000 miles We have gone through the engine, changed all the plugs and checked everything but the car will not turn over. There is no spark. All of the sensors have been checked, fuel filter was changed, in short everything has been changed except the pcv value. Could you please help, we are scratching our heads.

tries turning over but no spark, replaced plugs, fuel filter, crank switch, ignition coil board. Originally died and wouldn't start, fired up several hours later and several times after that. Now back to nothing.