Are you getting the 500 error everywhere now, or only when you specifically visit the Install/Home screen? That is, does the root URL continue to give you that
404 error while other pages time out? Are you seeing any errors in your Apache error log? What platform are you using? This problem could be a variety of different things, including a missing mod_rewrite plugin for Apache, a permission issue on disk, etc.
If you can answer some of the above questions, that might help narrow down the issue.