If replacing the motherboard transfer the four thermal pads on the underside of the motherboard to your new motherboard.

Motherboard remains.

The DVD drive and the motherboard are "married" when they leave the factory. If you replace one you must replace the other. If you put any old DVD drive onto a motherboard that it is not "married" to it will only play DVDs, no games. It is possible to alter the keys so that they match.