Installed AUCTeX with ELPA, but it's not loading

[Kai Großjohann]

I've installed AUCTeX with ELPA, that is, I've done
M-x package-install RET auctex RET
This seems to have executed successfully, and I was able to use AUCTeX
in the same Emacs session.

Then I started Emacs again, but AUCTeX was not loaded.  There is no
message that indicates what might be wrong.  "--debug-init" is not
helpful, either.

I am using Emacs 24.3 from MacPorts.  My ~/.emacs file is not empty, but
simple enough: it defines a few functions, sets a few variables, binds a
few keys.  It does not modify load-path.

The symptom I'm seeing is that latex-mode is from tex-mode.el.

How do I figure out what went wrong?

Kai