Check for spark at the plug wires while the starter cranks. If there is no spark, replace the crankshaft position sensor.
If there is spark at the plugs; buy a "noid light" from an auto parts store, and connect this tool to the wires for the fuel injectors. If the light does not flash while the motor cranks; replace the camshaft position sensor.
You can also test the camshaft position sensor by spraying starting fluid in the throttle body air inlet, and seeing if that makes the engine fire briefly when cranked. If starting fluid helps the starting; replace the camshaft position sensor.
If neither of the above tests helps; run a compression test on the motor. If the compression in all cylinders is less than 130 psi; the timing chain has broken or jumped out of position.