1998 Chevy Blazer won't crank

Other Category problem
1998 Chevy Blazer Engine Size unknown Four Wheel Drive Automatic 48,000 miles

When I turn my key to start the blazer I hear the buzzing noise and that's it. The mechanic got it started somehow. I drove the Blazer for 2 days was unloading it after shopping while listening to the radio got back in the car and it wouldn't start again. Now my mechanic is stuck I need my car back do you have any ideas? The battery is brand new. He pulled the starter out and had it checked, he then checked all of the relay things and has determined that he doesn't know but he is checking into it. Any thoughts