I have recently had this problem and found some help in an old thread. In the end I sorted it out so thought I would share for others just finding themselves in the same position.
Follow the below.
Power up NDS and once running normally press the Aux-i-Disp, this turns on programming (I think)
Press Aux-i-9 - this gets the remote navigation keys working well for the NDS, but the pre amp volume control doesn’t work.
Press Aux-i-1 - this gets the Pre Amp volume working, but not NDS navigation.
The code you want seems to be 21
So, after Aux-i-Disp, press Press Aux-i-1, and straightaway Press Aux-i-2.
This worked for me.
Note: If you go into the NDS Settings menu, and then Factory Settings.
Select the. Handset IR Monitor option
Press Play to start the Test
Press any key on the Remote
It should say RC System Code: 21
I managed to get a code 21 by pressing different key sequences and, as above, managed to get everything working as before the screen change.
Hope this may be of help for someone.