If nothing happens when you turn the ignition key to the "Start" position, it means that the starter motor doesn't turn over the engine. Most commonly this could be caused by a low/dead battery or there is no connection between the battery and starter.
Check/scan for any stored codes - the check engine light does not have to be illuminated for a fault code to be stored.
Check for these conditions:
Battery condition: loaded and unloaded, with alternator and fan/blower motor on 'High' speed,
Check all the main connections in the positive red cable from the battery to the fuse/relay box. Loosen
and clean, then retighten. Connections of main power lines may oxidize and lose the connection.
Air intake vacuum leak,
Dirty / contaminated mass airflow sensor,
MAF (mass air flow) sensor response,
Fuel rail pressure about 500 psi at idle and 1800 psi at 3500 rpm
Fuel line pressure from tank between 45 and 75 psi
Engine vacuum @ normal idle speeds should be 19-21 Hg and steady gauge needle reading. Should be steady throughout the RPM range and engine load.
Check for correct spark at the spark plugs - and at the ignition coil output side.
Faulty Body Control Module (BCM),
Reference the owners manual; and the ignition has a sensor built in that recognizes the key and a small microchip inside of the key housing.
If the key or that chip is damaged, the car WILL NOT START or turnover. This can be predetermined if your dashboard has a symbol that has a Car w/ Lock lit up.
Reference the TSB service bulletin:
GM has a technical service bulletin (TSB #02-06-03-008D) that covers all models dating back to 1990. It simply states that low volts/dim lights at idle may occur normally under certain conditions. The most common factor is a good battery being at a low state of charge due to infrequent use of the truck, or extended idling (low engine rpm).
An alternator puts out its lowest amount of amperage (current flow) at idle, because it's spinning so slowly. At idle, the engine and alternator are at their highest operating temperatures. The heat also normally hampers alternator output.
Another possible cause is the load on the charging system. What do you have turned on? Some high loads come from the headlights, blower motor, rear defogger, heated seats, and so on.
Problems to look out for include poor electrical connections anywhere in the system. This includes the battery cables, wiring to the fuse box, circuits to the alternator, and engine-to-chassis grounds. Also, be sure you've installed the correct capacity battery.