2004 Chevrolet Avalanche

Electrical problem
2004 Chevy Avalanche V8 Two Wheel Drive Automatic 64000 miles

What does the illuminated symbol of a lock and car mean on my 2004 Chevrolet Avalanche. Once symbol appeared unable to start engine. How can I reset?
February 14, 2010.

That is indicating the Anti Theft system is engaged. If could be for many reasons. I hate to say it, but a dealer is the only place that will have the proper test equipment to diagnose the problem. If you have a different key, try it. Sometimes the sensor in the key goes bad. If that doesn't help, then you need to see a dealer.