How do i unlock my jvc th-m505 dvd digital theater system?

You cannot lock the eject system of this multi CD player. You must be having a jammed mechanism because of dislocation of CD's. Take professional help or else open the top cover and see if there are any loose discs inside. Remove them and try ejecting the system once again. Remember to unplug the power when you open the system.

Given that this system sells for under $100.00, I can tell you it will cost you more to repair it then it would to purchase a new system. I was able to find a comparable one from JVC here : http://cgi.ebay.com/NEW-JVC-TH-S11B-HOME-THEATER-SYSTEM-205-WATTS-DVD-MP3_W0QQitemZ110441308049QQcmdZViewItemQQptZHome_Theater_in_a_Box?hash=item19b6d09f91

while unit is off hold the stop button until it says unlocked

If you are unable to get the tray of the dvd player open either the player will have a hole in front for you to stick a (I use a straightened out paper clip) into and press in towards the dvd player. It will manually open the drive so you can retrieve your dvd or there will be enough of a lip on the tray door you can grab it and pull it open manually. Then I would try unplugging the player and waiting a few minutes and plugging it back in and you might get lucky and it may never happen again. Good luck . Hope it works.

While the system is off

Press and hold the stop button and disc one open tray button at same time
It will say unlocked and then power up and you are good to go
Hope this helps i just unlocked mine got info from jvc user manual on website this link is the pdf
http://resources.jvc.com/Resources/00/00/95/LVT1147-001C.pdf

To unlock the JVC TH-C5 disc tray is by having the system off and at the same time hold the stop button and eject button until it says, "Unlocked". 

On the unit, press the stop button and the cd eject button at the same time. The screen will say locked still. Release them and press them together again at the same time. The screen will now read unlocked. You can then eject the cd.

instruction book says: on the center unit ONLY WHILE UNIT IS OFF there is a button with a square under it (on top of unit) press & hold also press & hold disc 1 eject button (arrow pointing up). The system turns on & "UNLOCK" appears on the display window.

disassemble the unit and eject manually

Turn the unit off with the power button on the unit (not the wall)
Press and hold Stop & Eject at the same time
The unit should power on and tell you it's unlocked.