Xen virtual console successfully installed as ttyS0?
 

I want to use my serial port but something called Xen is in my way. What is it and how do I get my serial port back?

Xen is like vmware - a virtualisation package. The idea is to split services down between various virtual machines, so if, for example, your mailer is compromised, the attacker only gets control of a bare system with a mailer in it, and not the entire box. It lets you use a server more efficiently, and more fully.

look at the /etc/rc.d/ scripts and you should be able to stop it, and prevent it restarting.