Domain behavior

not sure where to put this, so i’ll put it here, since this is where i normally post. i’m using cs3 with php and sql to create a member login, where once you login it shows your picture and info, etc… when you go to the website, using the www. prefix, the login works fine. when you go to the website without using the www. prefix, the “thinking” loop runs endlessly without ever logging in. any ideas what would cause this? i don’t want the website to not work whenever somebody lazy (like myself) doesn’t type the prefix.