What could cause norstar m7208 phone to not receive incoming calls

If you have lines appearing on your phone and they don't ring you need to program lines to ring. This type of programming is done from a M7310 phone. Page 323 of this manual shows how to program this on a NorthStar MICS Ver 6 phone system.
http://pdf.textfiles.com/manuals/TELECOM-F-R/Nortel%20MICS%20System%20Installer%20Guide%206.1.pdf

Enter the programming mode : Feature **266344
Password:266344
You will have 4 programming buttons on your phone, normally the 2 top left and 2 top right of the 2 vertical rows.
top left = move up one level
lower left = back
top right = select
lower right = next
once you enter the programming mode press next to "Terminals and Sets"
press select
enter your extension number
press select
press next to "Line Access"
press select
press next to "Line Assignment"
press select
use the next key to go to the line you want and use the soft-key below the display to change it from "Appear" to "Appear and Ring"