My WordPress Blog no longer works. When I try to view the blog's home page, it makes me download an empty .php file. When I use the control panel, I can't access any sections or the same thing happens. I have error messages saying 'Method not Allowed' and 'The requested method POST is not allowed for the URL /blog/wp-admin/index-extra.php' all over the page.
Is there any way to fix this, or to reinstall my blog without losing all my files?