I just got a brand new mac pro. I opened the cd drive with the eject button on the keyboard, and then went to close it the same way, the cd drive goes in, but the metal gate doesn't come back up. What can i do?
It's likely the case will have to be replaced. I've fixed this before by lightly tapping on the area below the gate, but it's a recurring thing.
You can also slide the optical drive housing out and take a look at the mechanism that raises and lowers the gate. Try manually pulling it up and down a few times.
In the attached image, you can see the cover hidden behind the outer "mesh" of the case, below the CD tray opening. It is supposed to snap back up from there when the CD tray hits those little hinges. Sometimes it gets gummed up, and it needs to be nudged to snap back up.
Solution: I was able to fix the problem by pushing on the hinges, as shown below.
If you are unable to nudge it out of place in this manner, it's likely really stuck. You'd probably want to remove it from the case and examine it. It might need cleaning: either blowing dust away with compressed air or gentle scrubbing with a toothbrush. If it's oily or sticky, you might want to use a tiny bit of warm water, even less soap, and scrub gently with a toothbrush or paper towel (let it dry completely before connecting it to power!). You might find that the spring mechanism is broken or missing, in which case you'd need to replace those parts.
Worst case scenario: bring it your local Apple Store or authorized retail/repair center and see if they can fix it.