If nothing happens when you turn the key, it is a problem in the starting system. I'm disappointed in your mechanic. It is a trail of where the power stops. You need to find a technican capable of trouble shooting a "no crank" condition. I can guess over the net only. I assume your battery is good and fuly charged, I also assume the cables are clean, tight and have solid continuity. The ignition switch appears to be transferring power based on the buzzing. Is power getting to the starter? If it is, you may need a starter motor.
Thursday, May 17th, 2007 AT 7:10 PM