by jackie fitts.
Finally found the error! The triangles opening/closing the menu were not working on the home page. No permissions at all (000) were set on /theme/yui_combo.php.
I had installed Moodle by uploading the zip (version 24) to a subdirectory, then extracting it on the server - and I guess permissions don't always come out correctly that way (?)
Hoping there are no other 000 permissions in other files, but for me, this is the answer to this issue.