browser doesn't stop loading

Hi,

I need your help to solve a big problem: randomly, when I visit several websites on my server, the browser doesn't stop loading the page, during 1 or 2 minutes; if I stop the loading and I refresh the page this is loaded instantly. I don't understand what is the problem.

My configuration: dedicated server Intel Xeon E5-1620v2 at 3,7Ghz, 64 GB Ram, 2x3 TB sata3 hd, bandwith at 500 Mbits, CentOS 6.6 64 bit, DirectAdmin with Custombuild 2.

Installed software: Apache 2.4.10, DirectAdmin 1.47.0, Exim 4.84, MySQL 5.6.22, Named 9.8.2rc1, dovecot 2.2.15, Php 5.3.29, suhosin 0.9.37.1, suPHP 0.7.2

Normally, mysql uses 240/400 Mb and apache 20/80 Mb.



This server was an upgrade from another less powerful but with Custombuild 1.2 and all sites worked fine.



I'm not an expert and I don't know where I can try to find the solution. My provider thinks the problem could be in the caching or something similar. But I don't use caching tools.

Please, could anyone help me to solve this problem? Which log you suggest to see?

Thank you very much

Regards

browser doesn't stop loading