I don't know your car, but a really grinding noise when turning the key (ever heart somebody try to start the car while engine was already running?) is the starter not catching the ringgear as the gear is worn out on some part.
In front of the bellhousing is a little window that can be opened and then you can see part of the ringgear. Take off the two bolts and the cover. Have someone turn the engine slowly (or use a large screwdriver as I saw the MB mechanic do when he showed me the chewed up ringgear on my car.
Hope yours is something else.