Step one: Unplug power, plug it back in. Should force reset. Press eject.
If no go, move onto step two: Take a credit card and slide it underneath the cartridge as you would when swiping the card at a gas pump. The will manually eject it. Unplug and replug the unit again, and then insert an the cartridge completely empty and let it cycle through. Then eject and load CDs.
If that doesn't work, come back and there are more options, but I don't feel like typing them and one of those will more than likely fix it.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>