CD tray won't open. What can I do?
Does
sudo umount /dev/cdrom
sudo eject /dev/cdrom
work?
If not can you eject the CD whilst the PC is at the BIOS screen?
Try hdparm -L 0 /dev/cdrom, and then eject?
Try sticking a needle or a pin in the small hole from the CD drive. That should get it.
Maybe try using a Live CD and then ejecting. Might help determine if it's a bug with Ubuntu, or your installation.