How is your DVD drive connected?
As a slave device on your primary IDE channel (together with your hard drive) or, on its own IDE (secondary) channel?
Try the following:
Connect your DVD drive to your secondary IDE channel by connecting the end of the cable to your drive and set the jumper setting on your DVD drive to "master".
If that doesn't work, change the jumper setting to "cable select".
If that doesn't work, connect your DVD drive as a slave device on your primary IDE channel (the connector in the middle of the cable) and set the jumper to "slave" and, if still giving problems, to "cable select".
I've also had some DVD drives in the past that wouldn't work together with other devices on the same IDE channel.
Also, swop out your IDE cable (it might be faulty) but, this isn't likely the problem.