All Pages redirect to home page

Hi,

I've been using drupal successfully for several months, and this strange occurrence popped out all the sudden. Any link that goes to another drupal page will kick me back to the home page. This is trouble because I can't even get to the login page. I should reiterate on 'link'; If I go directly to the page this still happens (user/login) doesn't work. I'm not sure when it started happening, but it happens on all browsers, regardless of cookie/cache settings and after clearing them. I tried running update.php, and I cleared the caches in the database manually. At first I thought it was phpbbforum integration module, then I disabled that in the database. It is still happening, and no resource that I've found on drupal--or elsewhere--applies to my situation. The closest thing is the 'unable to login' pages, yet none of the fixes worked. I am getting desperate here and I don't want to resort to a backup, because then we learn nothing from this bug, right? =P

Anything anyone knows, have dug up or can contribute would be immensely appreciated.

Thanks,

JD