Caddie not start and why?

If the starter engages and spins the motor try turning the switch off and allow at least 3 seconds and then switch on again but do not engage the starter, do this 3 times and if it starts you have some electrical issue and could be several things. When you switch to the off position you should here the fuel pump start and run for 3 sec. After the third on off cycle you should have ample fuel pressure to satisfy the computer to allow the engine to start and you should look for the cause. In my case after changing the fuel pump and the fuel gauge sending unit it cleared the problem. I think it was the sending unit but my Escalade has both as one unit mounted in the tank, not extreamlly difficult but time consuming and argraviting. Need to follow good safety rules to raise the rear end up high enough to get tank from under the car. Hope this helps, good luck and be safe