I have a 2004 chevy 2500HD 2wd, gas. I can get the engine to turn over. First I changed the battery, not it. Then I pulled the stater, the stater is good. Used a volt meter and found i I'm not getting any voltage to the started when I turn the key. I have conformed that the ignition switch is good. With the key in the start position I have 12v on the positive side of the start relay that is under the hood in the fuse box. I checked the relay and it is good. I jumper the contact and the starter turns over the engine. I don't get a ground to the negative side of the start relay. It is a pink wire that looks like it goes to the computer that is under the battery. With everything connected I set in the driver seat, key off, the door locks work. Key in the on position, the locks work, windows go up and down. The lights on the dash and daytime lights come on. I turn the key to the start position and nothing happens. Release the key back to the on position. The lights stay on but now the door locks and windows don't work. The yellow light on the instrument panel that looks like a truck with a closed lock comes on for a moment but doesn't stay on. Using my OBD2 reader with the key in the on position, the reader will not link up to the truck. I am down to one of two items either the vehicle security lockout or the computer. Any help before I spend a lot?

 

Sounds like a security lock out to me as well. CPU failure can cause a security lockout from what my research seems to say.

 

Good news. I finally fixed it. This truck sits in the barn when it's not being used. This morning I when to open the hood and a mouse was on the motor. So I took a wild guess a started looking. From under the passenger side looking up I found a bare, broken wire. From the top, center of the transition housing. I spliced the wire and grounded it. Fired right up! Damn rats.

 

...yup, a bad ground will do it too.