I had the same problem with a comparable device. It turned out that the drive belt that operates the ejection mechanism wears out or breaks.
To get at it you need to do the following:
1. remove device cover
2. remove the identification cover on the front of the DVD tray. This may be tricky if you can't open the tray. You need to find a way, because otherwise you can't remove the DVD unit, at least not on my unit.
3. remove the DVD unit by detaching the cables and removing four screws.
4. remove the two top screws on the DVD unit
5. remove the front top cover of the DVD unit by pushing the two tabs on the top of the unit, near the front.
6. Now remove the tray, by pulling it out as far as it goes and then pressing two tabs on either side of the tray. These tabs look like this:
7. Now you get at the drive belt. Originally it was black; I replaced it (temporarily) with a red one in the picture below:
8. Now put everything back together.