You provided hardly no details of the setup you have. It certainly helps us to help you to provide such.
The new DVD drive if completely disconnected will allow the system to boot as before? If not, then some connection(s), etc., may have been done or improper setup. Review the work and see what that maybe. Again, we have no clue if this is SATA or IDE type drive. If no manual came with the new DVD drive, check their support website and find the DVD model# and get the install manual or guide. If so needed, you should verify in the bios area, what if it sees the new DVD when connected, what it reports during boot-up after reconnecting the DVD properly. If it still reboots on its own, then report back.