If you look on the front panel of the drive then you will see a pinhole sized hole. Insert a straightened paper clip or similar into the hole and the door will slide open. If it still fails to work after that then its time for a new drive. At least you can get whatever disk is in there out in the meantime.
you may have to shake the drive or pull it from the pc case and turn the drive upside down if there a cd and it fell out of the tray.
to much pressure and the disk will snap. if the drive gears have broken for the tray..most cd-roms take the four screws out on the sides of the drive and the top case of the drive will come off. you be able to get the cd out that way.