Open Tools | Customize and click on Keyboard... Select any command and enter
Alt+Ctrl+D in the "Press new shortcut key" box. Then look to see what is
given for "Currently assigned to." If you get "[unassigned]," then the key
assignment has somehow been lost.
In that case, select the Insert category, scroll down to InsertEndnoteNow,
and reassign Alt+Ctrl+D to the command.
If the assignment is already correct, it may be that some other application
is preempting the command, and you'll have to do some research to see where
the interference is coming from. Alternatively, you can assign a different
keyboard shortcut to InsertEndnoteNow (by default Alt+Ctrl+N is unassigned,
and Alt+Ctrl+E is (or may be) assigned to the euro character; either of
those could be substituted.
