[alvaroag]

What are you running on the server prior to reboot? Maybe you are installing some package that enables iptables or an iptables based firewall. Have you tried a simple reboot after installation, without doing anything else? Does the server answers ping after reboot?

Other possibility. Try booting into rescue mode after an unsuccessfull reboot, and check the logs for anything to do with sshd and/or firewall.

[Sledger]

The CentOS 7 gets installed perfectly but as soon as your reboot it stops listening to SSH. I have tested this over 2 servers today & reinstalled each server 5+ times to make sure.