2000 buick lesabre intermittent start

I have a 2000 buick Lesabre. I go to work Ok, and then go to the garage turn the key lights go on nothing starts, no noise. I slam the door open the hood and slam it then it starts. I took it to the mechanic and it starts every time! lights on dash go on and off intermittently.

any ideas?

Welcome to AF. Clean and tighten all grounds and battery connections, battery is under the rear seat.

Wow this one almost sounds like my 1995 LeSabre intermittent start problem.
But closing doors and hoods doesn't seem to help mine, it really has a mind of its own.