Help. Have a A6 2004
 

I went to the store and while pulling into parking lot car turned off so I put it back in park started up fine went to store then back home hours later I went out to get dinner left car running outside grabbed my food got in my car went to drive moved 3 feet and shut off again so I tried starting it and it' like it wants to start for a brief second then turns off tried starting a few more times it just starts for a split second then off so left it in park2lot went home came few hours later now it just cranks wondering if it''s a starter.. just looking for some insight before it gets to mechanic shop.. TIA