General help

Last week everything was fine. I started enrolling students in a course, and suddenly things started to get funky. I noticed I no longer had an admin block on the homepage. Now the homepage won't show up at all... the students can still log on fine, but not all assignment mods are working. I can see classes if I type in the direct address, but when I click to turn on editing, all of the assignments disappear. I can't see any admin pages even if I type them in directly. When I go to:

http://lhsvisualarts.com/moodle/admin/roles/assign.php

I get the following message:

A required parameter (contextid) was missing

Any advice would be greatly appreciated!