Oldsmobile/Buick Repair: car not starting, oldsmobile alero, intermittent fault

Question
Today is the 3rd time this has happened.  The people who we take it too don't know either.  It will start for a while.  It will fire but not turn over.  There is plenty of juice in the battery.  The last 2 times, by the time the repair shop went out to pull it in there shop, it started.  They noticed this time, that the anti theft light was on, and thought maybe it might be the anti-theft system not letting it start.  They then left the key on for 30 minutes (which I guess resets everything) and then it started.  My husband says though that it backfires sometimes when it does it.  We have had an alternator, starter, new battery put on.  This is a 2002 oldsmobile alero - 2 door - 4 cyclinder.   Please help if you can.  We have been out so much money.  This is happening every 2 to 3 weeks.

Answer
You need to have your anti-theft system tested as this is the most likely suspect as there is an intermittent fault due to the light illuminating on the dash.

There are numerous sensors and relays in the anti-theft system that will need to be tested via special equipment.