Assuming you know your way around comps:
1. Does the DVD show in the post messages?
2. Is the DVD present on one of the IDE channels in the BIOS?
3. Is the DVD present in Device Manager (right-click My Computer - Properties - Hardware)?
If present in DM, remove the IDE channel that it's on (under IDE ATA/ATAPI Controllers) and reboot. This will freshly install the drivers for it.
If it's not in the BIOS, crack open your box and make sure the IDE and power attachments are firmly seated (check mobo connection too).
Still no luck after all that, remove it and take it to a friends' comp and "temporarily" install it there. See if it works. If it does, then there is a Registry issue.
Get back to us.