Using a proxy may cause Blizzard titles to experience issues with connection, installation, or patching. Follow the steps for your operating system below to disable your proxy settings.
Press Windows Key + R.
Type inetcpl.cpl into the Run window.
Click the Connections tab.
Select Never dial a connection (if available).
Click LAN settings.
Uncheck Use a proxy server for your LAN.
If this setting is already unchecked, try to toggle Automatically detect settings.
Note: If you've never used a proxy server, these settings can be enabled or activated by malware without your knowledge. If either of the proxy settings are checked, be sure to run antivirus software after unchecking them.
Disabling Offline Mode in Internet Explorer (version 10 and below)
Open Internet Explorer.
Press Alt + F.
Uncheck Work Offline.
Choose Apple menu > System Preferences, then click Network.