Problms with my 1997 pontiac grand prix se plez help?

i will keep this short as possible ok my car has been having problems with not wanting to start key would get stuck in ignition the check engine light is on so i hooked up diagnostic tool code reader it keeps telling me its not conected i tryd anther veical to make shure it wasn't my macine and it worked fine but go back to the grand prix and and ses not connected to vehicle it just started a few days ago having problems going in revers it wont go into gear some times drive works fine it will eventual go in to revers but makes a big clunk sound so i took it in to shop they looked at it for ten min and sed transmition is going out idk if i be leave that any advice or any clue why my code reader wont Connect pl ez help