Memory upgrade is what solved the problem, (+reinstall) enabling swap might have solved it too though.
Admin/Mod category disappeared.
So one of my mod categories has disappeared. It's available to admins and moderators. No one else can view it.
Trouble is, it no longer appears in categories.tpl. I can access the topics and post, just doesn't appear in the category list.
There is a bug in the category module (in 0.7). As a temporary solution I had to activate all "inactive" categories (and change the permissions on them to be invisible for the normal registered users).
@hek Don't have any inactive categories unfortunately.
Fixed it, set it as a child category, then back again.