I installed a new ignition switch but it wont start

ignition switch ? Key & lock cylinder or the electrical switch ? Do you know how to test the ignition switch electrical circuit's using a volt meter ,hook up a professional scanner an check for module communications . Free wiring diagrams here http://www.bbbind.com/free-tsb . Did you get the switch installed correctly ?
How to Replace Your Ignition Switch in 2003 2006 GMC and Chevy truck and...

1999 you had to put ignition on and wait 10 minutes until security light stop flashing and came solid now it is program .Switch must be brand new ,from scrap wont work, 2004 ?

I'm not a car mechanic, but, it sounds like you might want to check the fuse to the ignition switch, and, if that fails, it might be a problem with the Start Safety Switch on the transmission. Good luck.

sound like ignition problem let dealership check it out.could have fault in new switch or wrong type switch.ignition switch install wrong.

Check the ignition switch, and the wiring to the starter solenoid. Get someone to turn the key to the crank (start) position and check for voltage at the starter solinoid. Check the starter relay and all fuses.

if you have installed a new battery and it still wont start it is most likely the starter that went out and will need replaced. hope this helped

The ignition key and the ignition switch are part of the anti theft security system. The anti theft system has been triggered and the ignition system will no longer start the car. The only way to get it working again is to take it to a dealership and have them install a new ignition switch with matching key and control module. These three parts plus labor will cost you at least $1,000.00.

check the rear of your trunk driver side like if your going to change rear brake light do you have a gas override switch wich starts the gas pump its a restart button you have to remove the panel as if your going to take off tail light on driver side rear its an emergency shut off.

pcm one of your computers

You need to establish that you have 12v in the battery and that all connections are clean and secure. Lights horn etc do not give you voltage verification...your starter uses more amperage than anything else in the car. Once you are certain that everything is OK, check for 12v at the small wire on the starter with the key turned to start. If no volts, check the neutral safety switch or clutch switch Then check ignition switch for power in/out.