Usually the server could be online, but some parts of server software not. In this case you have no need in cold reboot of entire server, we recommend you graceful reboot of the services. If you are running an ISP Manager 5 on Linux server you should run:
/usr/local/mgr5/sbin/mgrctl -m ispmgr exit
or
killall core
This procedure is often applied after configs modification:
/usr/local/mgr5/etc/ispmgr.conf