Cirtrix Xen and Centos 6.2

I have a xenserver it keeps crashing. After 2 day i need to find out why ? Also on this server is a centos 6.2 with plesk. It was running varnish but the config is very hard to work with on centos and the updates keep taking it down. I need the hosting config put back to standard plesk nginx and varnish removed. Here are Investigate xenserver crash reason remove [login to view URL] (old as now roundcube comes with Plesk) remove varnish configure nginx with php-fpm optimize centos server was running a 2 core and and 6 gig or ram now is running 4 core and 16 gig not changes were made to os. Update centos Yum to a good repo. No updates seem to comming through . Or at least see whats going on.