3.1 Update – no more Authors?

Have you tried:

– working through the solutions suggested in Troubleshooting WordPress 3.1 – Master List

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the Twenty Ten theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

3.1 hides some screen options on posts & pages edit screens by default. Just turn on the ones you want.
More info here: https://ottopress.com/2011/wp-quickie-metaboxes/

Otto,

Thanks for the reply and the link. That was it! I never knew I could update the screen options. Thanks so much for an easy fix!