2000 chevy silverado 2500hd With 6.0 motor, will not turn over.

so the starter is getting power when you hit the key ? You tested this with a multi tester or are you assuming ? I guess you have to pull the plugs and see if the motor will turn over by hand , unless it's seized

Thank you for the response, No the starter is not getting power from the key. I checked the starter by removed the starter relay and use a jumper wire on the pin openings for 30 to 87 to run the starter motor and it ran good and strong and was turning the motor over but would not start. Then I swapped around 2 other relays that are exactly the same to compair and see if the relay was bad or not and is good. I did notice that after changing the Ignition switch and key cylinder that my head lights and tail light come on when I turn the key on. I just bought the truck from my son and he tells me the security light never worked in the dash and is still not working. I guess my next step would be to change the safety neutral switch or have you any other ideas?

check into the vehicles stock security passlock as they call it, it can create many undesirable instances. but the fact that you changed out ignition would definetly have something to do with that or possibly if your key has a chip but im pretty positive it does not........hope that helps....im sure it is somehow part of your problem, just got to do some research.