Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, consider the likely possibility of an internal hardware issue hence the disc tray would not eject particularly if an error message is displayed something like "CHGR ERR". If so, then the Panasonic SA-PT673 would have to be opened up for visual inspection, mechanical/voltage/continuity/resistance checks, confirm faults and effect repairs.
If comfortably able and feel safe to do so, are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even perhaps a soldering iron?