I can't access the Plesk Panel on both ports 8880 and 8443 on my server.

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