You can open it using an unbent paper clip that you insert in a tiny hole just under the tray. That hole is just whide enough for a paper clip.
Here's how I succesfully fixed a CD and a DVD drives that had that same problem:
To possibly fix it, you need to open the computer and remove the drive.
Next, you need to open the CD unit itself.
Manualy operate the tray in and out a few times and put everything back in place.
Reconnect the drive.
Power up and test.
If it still don't work, get a new one. CD/DVD writers are relatively cheap.
Just be sure that you get a new one that have the same connector as your actual one. ATA/IDE one use a ribbon cable with 2 connectors, while SATA ones use a small cable with a single connector.
Electro
August 2013