Well you've got power running, so check if the cables are connected.
Since you are running Windows Vista you should check the device manager. (Control Panel > Hardware & Sound > Device Manager)
Check under DVD/CD-ROM Drives if the devices are displayed.
If they don't show up try Action > Scan for Hardware changes
If they do show up right click the devices and select update drivers. Maybe reboot and try again.
The last thing that may be happening is that they work as normal, but the problem is that Disk Management doesn't assign a drive letter to the drives. To fix this issue you should start the Disk Manager.
Start > Search for "Windows Disk Management"
Then scroll down to the drives and see if they get a drive letter assigned. If they don't right click them and select "Assign drive letter and Paths" then select the drive letter of your choice. Now you should get promted.