I administer a private forum (no new registrations). I changed the start module to NEWBB yesterday afternoon & things seemed to work fine. Today, none of my users can get on the site - we get a blank start page (with url including /modules/newbb). Worse, I can't load admin.php, because I'm not logged in (it boots me back to the blank start page).

Any suggestions aside from starting from scratch??

Have you tried the http://www.yoursite.com/user.php in order to log-in?