Did you flash the 0800 benq firmware? Does your bios see the dvd drive? If it does then I'd try reflashing, then rebooting and checking in device manager.
If it's not seen, check that the drive is actually on (can be ejected) - hopefully you added an eject switch! If it's not on, check your soldering. Especially the 3.3V regulator. Test that you're getting 3.3V on pin 3 or your spdt switch.
Also try a different sata port, or get a sata to usb cable and externalize it.
Hopefully I could be of some help, the first time I did this I struggled, and eventually found that my soldering was a bit dodge