Some ideas
Try this first as it's software:
Go into the control panel, system. hardware, device manager, IDE ATA/ATAPI controllers, and open whichever IDE channel the DVD is on. Go to advanced settings. Change the transfer mode of the device to PIO mode or DMA mode alternately and see if it affects the drive. Maybe play around with the auto detection to. If you know how you can also mess with the UDMA/PIO settings in the motherboard BIOS, but start with the Windows driver settings.
Swap the cable end between the CDROM and DVD and see if anything changes (checking for cable issues and since you know the cdrom works, if it's a cable issue, the DVD will now work and the CDROM wont). Bonus is if they both work now anyway, in which case, don't mess with it :-).
Check for a newer motherboard BIOS. Also check for the latest firmware for the DVD from the manufacturer's website. They tend to be flashable also and the manufacturer will have a util for flashing it.
So you know, I have a DVDROM that when flashed with the latest firmware, the motherboard BIOS no longer recognizes it, but windows still does and it works. Even though it works still works with the latest DVDROM firmware, I went back to the older firmware (that the motherboard BIOS recognizes) just for safety.