Volvo: 2002 S60- doesnt start, inhibitor switch, charging system

Question
I've been having an ongoing problem of my 2002 S60 not starting.  Today, I drove for 30 minutes, parked and ran inside for 5 minutes and then came out and the car would not start.  Lights, radio, etc. all came on but the engine would not do anything.  did not hear it turn over or crank...it made no sound!  Same thing happened yesterday, but car ended up starting after about 5 minutes.  Today, had the car towed to a repair shop, but when it got there it started.  Also, I find that I am constantly replacing headlights, 3rd brake light, and tail lights.  Replaced numerous times.  Could there be something wrong electrically that is affecting both the lights and the engine not starting?  all thoughts would be much appreciated!  I am getting super frustrated!  

Answer
Hi Susie,first of all have the charging system checked out,it is possible that the voltage regulator in the alternator is malfunctioning,it could be the same problem with starting but that can also be faulty starter or the inhibitor switch on the transmission.