Is your dvd drive an IDE/PATA interface drive? Does it hook up to a large, wide, flat cable? If so, you have to make sure that the little jumper on the back of the drive is set correctly. Look on the back of the old drive and see what the setting is with it. The jumper is a small piece of plastic with metal inside, that connects two pins.
There are three settings for the little jumper, Cable Select, Master and Slave. If you hooked up the drive to the very end of the IDE cable, set the jumper to Master. If you hooked up to the middle connector, set it to Slave. Cable Select allows the computer to determine this, and it works for the vast majority of computers, but some don't work well with CS (usually very old computers).
You also have to plug in the power cable, but it can only go on one way.