Have you tried this?
Ensure the child lock feature is disabled. (You've done that, but make sure it is)
Attempt to open the disc tray.
If the issue is not resolved, turn off the DVD player.
Unplug the power cord from the electrical outlet for 2 minutes.
Plug the power cord back into the electrical outlet.
If the disc tray still does not open, simultaneously press the POWER + STOP + EJECT buttons
If the disc tray still does not open, simultaneously press the DISC1 + STOP + EJECT buttons.
If none of the above works, you normally have to ship the unit to Sony to get it repaired. Small items like this are repaired at the factory nowadays.
If you have any questions, just ask
If you are finished, please press the ACCEPT button..