2005 astra 1.6 auto, gearbox is 'locking out' the engine?

can anyone tell me why the engine wont start on my 2005 astra. A knight in shining armour got it started again so I got it home, but it wouldn't start the next morning. He 'tapped' something a few times to free the gearbox selection which had locked out the engine from what I can remember!
does anyone know what I'm talking about, if you guys can help me I'd really appreciate it. debbie