At random times I cannot start my 2003 TrailBlazer. When I turn the key, the lights come up on the dash but it doesn't make any sounds like it's even trying to turn on. I cannot figure out what makes the difference when it does turn on. After 10 or so tries it works. I'm not sure if it's because I keep trying the ignition switch or the time it sits there before it works. Was only a problem every once in a while but yesterday it happened 5 times. Now the service engine light is on.

Get car scanned whenstarted-got to know if any bad codes--hav batt tested--do a tuneup-chec plug wires and distributer/coil area plus the rest of the electrics--ignition switch and module may be failin

This may be the antitheft system starting to fail in your vehicle. Very common on GM vehicles.The key has a transponder in it that communicates with the ignition, and then the ignition passes that signal on to the TDM (theft deterrent module) which allows your starter to start, if any of these parts fail to communicate, the system shuts down and the starter wont roll over. This link explains the problem, lists symptoms, and offers some DO IT YOURSELF solutions to the problem.

http://vatspasslockpasskeysecurityhelp.yolasite.com/

Trailblazers that are effected by faulty SECURITY systems
2002
2003
2004
2005
2006
2007
2008