Please check if you have tried to reach the system over the right protocol (https or http). If this is the case please verify that the ISPConfig system started before (with
on the command line, or just restart the ISPConfig system:
/etc/rc.d/init.d/ispconfig_server restart (RedHat/Mandrake)
/etc/init.d/ispconfig_server restart (SuSE)).
If this still does not work, then most probably your firewall (iptables or ipchains) is blocking port 81.