If you already have the list of proxies for your use, but you can't browse any websites at all, follow these steps to troubleshoot the issue.
In order to start using the proxies, you need to add your source IPs from which you will be accessing the proxies, otherwise you will be asked to enter your username and password.
Please click on Authorized IPs link and add your IPs to the list.
After you add the source IPs wait 30 minutes before using the proxies.
NOTE: If you are using the Socks protocol, please refresh the Socks each time you add the new IP to authorized list.