The most likely thing is a dead battery. Batteries don’t recover very often from a deep discharge.
The buzzing is due to the something switching on and off due to the battery voltage dropping each time it tries to supply power.
Check the battery voltage with all the lights on, if it is not over 12 volts after the full charge, then the battery is likely dead....
The pinion gear on the starter meshes with the flywheel. I was taught in college that an engine tends to stop with the flywheel in approximately the same spot. I don't remember the whys of it. But at any rate you may have damaged teeth on the flywheel. Removing the inspection plate the teeth can be inspected while turning engine by hand.