I am unable to access anything other than the front page of my site (IP Pages). All items cause a 403 error and I can't seem to figure out how to fix it.

Have you made any changes just prior to  this occuring, which may be related?

Do you have FURL rewrites enabled?

If so, check to be sure the lines supplied for the .htaccess file, haven't gone missing from the actual .htaccess file.

(Being able to see the main page, but getting 403 on any other pages, is a clue that this is the case.)