Anything .PHP Won’t Work/Page Not Found

Whenever I try to login, I can’t. It says page is not found. When people try to leave a comment, it says, “page not found”. When I try to edit a comment or a page, it says “page not found”. What is going on?! It was working yesterday & all of a sudden it just stopped working. I’ve uninstalled WordPress & reinstalled it at least 3 times. All of my hostees have no problem with their WordPress, it’s just mine. I don’t understand what is going on.

Any page that I have that has the file extension, .php, doesn’t work! Somebody please help. Thanks in advance.