警告:require()[function.require]:无法打开流:没有这样的文件或目录

This error is quite common and it generally means it can't find the file it's looking for, but I can see the file in the directory?!

Full error:

Warning: require(/home/coinsfut/public_html/files/core.php) [function.require]: failed to open stream: No such file or directory in /home/coinsfut/public_html/new/index.php on line 4

line 4 says:

require $_SERVER['DOCUMENT_ROOT']. "/files/core.php";

the site is hosting in /new

any ideas?

Check the warning again. You are trying to include

/home/coinsfut/public_html/files/core.php

when in fact you want

/home/coinsfut/public_html/new/files/core.php

Please try

require $_SERVER['DOCUMENT_ROOT']. "/new/files/core.php";

and it should work just fine.

Alternative you could use

require "files/core.php";

to include files in a relative sub-directory since your index.php is in "new" directory.