It's not possible to know what you did to lose your original
binding, so here's the basic upshot.
- Your customizations (as with keybindings) will be stored in
and any other elisp files you call from it.
- If it was a temporary change (i.e., you didn't make changes to
init file manually or through
customize), you can
just restart Emacs.
- If you did make changes to your
init file (intentionally
or not), the problem will persist into new Emacs sessions.
- If you have no idea what code in the
init file is causing
you to lose your binding, do the following:
- Start Emacs without your
init file (
emacs -Q) to
- Recursively bisect your
init file by successively
commenting out halves until you isolate the problematic lines.
For a given keybinding, you can find out what it calls with
KEY SEQUENCE, (where
C-h k calls
describe-key). For example,
you can try
C-h k C-c a.
For a given command, you can find out the keybindings with
C-h f calls
describe-function). For your
case, you can try
C-h f org-agenda to see what keybindings it has.
Note that the
org manual's node on
C-c a as a global keybinding to access
you're under no obligation to use that particular binding. If you
want to bind it again, you can follow it's suggestion with:
(global-set-key "\C-ca" 'org-agenda)
You can put that in your
scratch buffer and evaluate it, but it
should be somewhere in your
init file if you want it to persist
through Emacs sessions.
As an aside, the reason
C-c a is not a hard and fast binding is
that it runs against
keybinding conventions in Emacs,
one of which states:
C-c letter as a key in Lisp programs. Sequences
C-c and a letter (either upper or lower case)
are reserved for users; they are the only sequences reserved for
users, so do not block them.
More generally, have a look at the Emacs manual node on
Customizing Key Bindings
to find out how to bind keys as you like.