There are a lot of hosting companies that offering a great service for your WordPress, one of them is Yahoo! Small Business.
If you are using this hosting service and you also using WordPress, then you should get a problem like this one:
Every time you click on a post/page, the result always the same: error page not found. You already try all possibilities but the result is none, the error still exist
This problem is caused by the security of the Yahoo!. Their service is not allowing a file named .htaccess exist on your folder, even if that file is exist, that file will not be read by the server.
.htaccess file is needed by WordPress for permalinks, without this file WordPress permalinks will not working. So, that is the reason of why your post/page always return error page not found.
To fix this problem, go to WordPress dashboard → Settings → Permalinks
The default value of this option is default, change it become custom structure and put this code on the available form