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.