You should use a registration hack.
There is two here:
Nifty way:
http://mobileread.com/forums/showthread.php?t=87686
Goodspeed way:
http://mobileread.com/forums/showthread.php?t=87336
(You need usbNetwork Hack)
Then Do this if you want to do more:
http://mobileread.com/forums/showthread.php?t=95076
But why you got this type of Kindle DX now ? is it used ?