HP External to Internal

The disc tray in my exisiting DVD Writer has been broken in half. I have to replace this drive. I have a HP DVD840e which is external. I opened the case and installed it internally. The PC recognizes the drive in BIOS and WINXP. When I insert a disk it says “no disc”. I downlaoded firmware from HP for the exact drive, but still no operation. Am I missing something or can this not be done. I dont want to use external because it is really slow.