For being an Xbox360 technician there is one thing that I have found out.  And that's how the
key card that's located in the DVDROM is married to the mother board.
The key card in the DVDROM has a unique hexidecimal code that will be recognized
by only one Xbob360 mother board in the world.  This is set up durring the firm ware
programming.  And there are 3 or 4 different kinds of DVDROMs that were installed
into the Xbox360.

So, if you plan on changing out the DVDROM in your 360 you can't just change them out.
First, you have to identify which DVDROM you have.  Then get the same model.  Disassemble
both.  And swap the key cards.  Making sure that the same key card goes with 'its' game system
mother board.

So if you plan on selling or purchasing an Xbox360 mother board.  Make sure that its key card
or .bin (binary) file comes with it.  If only the .bin file is available make sure of what brand
DVDROM was in the unit.  Otherwise, the unit will never play a game and you'll have a
unit that's good for DVD movies and audio CD's only.
There are programs that enable you to change the key number in the key card.
This requires different techniques depending on the brand of DVDROM.
As well as a computer with a VIA chip set and open SATA ports.
Follow directions well.

In reality.  An Xbox.360 will recognize only a one of a kind key from the key card in the world.
I repair Xbox360 systems for a rental outfit.  And sometimes I get a unit that 'won't play games'.
And there is no way I can fix this cause I can't get the original DVDROM or the .bin file.
And of course.  The customer had been in the box and just changed out the DVDROM
without knowing the other necessary facts.  Resulting in no game play.
If someone knows a way around this please let me know with detailed directions.
I've looked all over for months and havn't found anything yet.
Mayby I can get a few more Xbox360's to play games.
I'm even seeking for a way to redo or reprogram the firmware for the 360.
Which would definatly get the key code programed for games.

I hope this helps you out.

Wiz.