Had no prior issues with this car! I went to the local Gm dealer, had a new ignition key made. Dealer used tool to check what key I needed, cut new key, I went and tried new key, no issues, car started fine! I gave this car to my son to drive, he drove car, shut off car, started it with no issues. He shut car off, went to start, nothing happened. I went to check out car, tried the original keys, no cranking at all. Car has new battery up to charge, has spark at the coil when i jump starter, I can hear fuel pump coming on, has pressure at the schrader valve. I Installed another starter, same issue. I checked the starter small wire with a test light while someone else held ignition switch in the cranking position, and the test light does not light up.I turn key on, and the SECURITY light flashes. I left key on for 1/2 hour, SECURITY light stays flashing! Any ideas what I need to check next or how to clear SECURITY issue so I can start car? What may of caused this problem in the first place? Thanks for anyone'* help!

Check the fuel injector fuse.

I by passed the vats system, using an original key placed between the 2 wires from the vats system, car starts up fine, only problem now is the security light stays on. thanks for responding!

When a new key is cut it will turn on the ignition and a security light will come on. It then locks out the new key. What you can try is found at PROGRAMYOURKEYS(dot)COM.
If I remember correctly all you need to do is use an original key to turn the ignition to ON (but do not start) wait for security light to go out. Remove the original key and within a couple of seconds insert the new cut key, turn to ON (again, do not start) then when security light goes out turn OFF and remove new key. It is now programmed to your car.
Eddie