It's likely the IPTABLES has the default settings and only SSH Port 22 is allowed.
- We suggest Putty a SSH client or similar to SSH connect to your server and issue this command "service iptables stop"
- You should be able to login to your control panel now either with http://your-ip-addresss:8880 or https://your-ip-address:8443.
- Complete the setup and license activation if you have not done so.
- Now, go to extension and activate the Firewall.
- Once you have activated the firewall successfully, default rules with the ports 8880 and 8443 will be enabled.
- Try accessing your Plesk Panel again and if you are still experiencing difficulties please write to our help desk for assistance.