The first thing is to look if real no instance of C::B is running. Some window-managers (or more exact their session-managers) try to restart programs that have been opened on last shutdown.
You can try to kill it if there is an instance running by either "killall codeblocks" or "killall -9 codeblocks" to force killing, or by "kill [-9] <pid_of_running_codeblocks_process>" .
If none is running you can have a look for "/tmp/codeblocks*", but that should not matter, even if it exists.
And normally on linux the tmp-directory is cleaned up on boot, so nothing should stay there from before your crash.
If that does not work, you can edit your "default.conf" in "~/.codeblocks/" and change
<SINGLE_INSTANCE bool="1" />
to
<SINGLE_INSTANCE bool="0" />
to allow multiple instances of C::B running at the same time.
If all that does not work try to delete (or better rename) the "~/.codeblocks/" directory.