Dvd tray stuck - Sony DVP-NS315 DVD Player

In the front of the DVD tray, look for a tiny hole. Straighten out a paper clip, push it into the hole and the tray may release.

What make and model DVD player?

if you look on the drawer for your dvd drive, you will see a little hole.If you push a pin in the hole the drawer will open.

take the top off the dvd player and see if something is stuck in the player. also a little bit of vasaline on the dvd door tracks helps for ease of movement

Is it jammed?
Still has a CD/DVD still in it?
Is so try cycling the power to see if it will kick it out.

Otherwise it's most likely a hardware problem like a bad tray motor, broken gear, or perhaps a bad/stuck switch on the tray assembly.

If it's still under warranty, call the manufacture technical or customer support for a possible replacement.

Replace the DVD drive. They are inexpensive and it's not worth your time to try and fix this drive...

Turn off the computer and then use the paper clip to open the DVD tray.
If this doesn't work, then something is jaming and stopping the tray from opening. In this case, remove the DVD drive and dismantle the drive (ie. remove the metal cover to reveal the internal components and remove the CD ot DVD disc.
If nothing works the the DVD drive is faulty and needs to be replaced, these drives are not expensive.

the tray is not catching (underneath the tray is ridges). unplug the dvd player from the wall for 5-10 min...plug back up and give the tray a lite push while tapping the open/close button

I had this happen when someone put a DVD in the tray when there was already one in there. I managed to pry the tray out to retreive the DVD's, but when I closed the tray it was stuck for good. I wouldn't bother doing this because you'd probably have to take the player apart for it to work again anyway.
I took it apart and found that the gears were thrown off from the jammed tray. If you have some mechanical ability, you should be able to see where it is off track. Most likely you would just have to snap the gears back in place, hopefully none of them broke. Also, when you have it apart, you can manually open and close the tray part to assure that it's corrected.