Electrical problem
1998 Chevy Blazer 6 cyl Four Wheel Drive Automatic 192000 miles

My blazer will start but shuts down after a few seconds. I have had it diagnosed and it keeps saying reprogram the security system. The mechanic tried to reprogram it multiple times, he changed the sensor in the ignition lock? and it still is not working. The fuel pump was tested for pressure and it reads 55. I am at my wits end and running out of money. Please help.

When you turn the key to the on position but not starting the engine -- does the security light blink?

When the key is turned in the ignition, the light on the dash for the security alarm stays on, it does not flash.

Your security system is called PASSLOCK. Being that the light is on, and not blinking, usually means that the passlock main box (the brain) has failed or has a problem. This should be diagnosed at a dealer, because they have the proper computer diagnostic scan tools.
If the mechanic changed the ignition switch with the security light on, and not flashing, then he or she probably does not have the proper diagnistic tool for your problem. They just shot in the dark hoping to fix the problem. This will cost you a lot of money - so take it to the dealer....

Thank you everyone who gave suggestions. My mechanic was able to get it running. It turns out the signal between passlock and the BCM was getting interupted (bad connection). He was able to fix it and scan it for any codes. Again, thank you everyone.