WP 3.0 Upgrade: Posts are 404 Not Found

I automatically upgraded to v3.0 from 2.9.2 and now all my posts are coming up “404 Not Found”. I can access the main page, but all sub-pages like “Contact Me” are inaccessible. I’ve tried manually upgrading but the problem persists. I’m assuming it’s something to do with .htaccess but I can’t seem to track down the exact cause. I have also tried deactivating all plugins. I can access Admin pages just fine.