1. Identify if you're running a proxy or not
Click on Start
In the search bar, type Proxy Settings
Select Proxy Settings (System Settings)
Under Manual Proxy Setup, if this is turned ON, you are running a proxy server.
2. If Proxy is used, disable the proxy server
Under Manual Proxy Setup, click on Set up
Set the toggle switch to OFF. Click Save.
3. Troubleshoot it as a security issue
Temporarily disable your firewall and any security app that might be running in the background.
4. Troubleshoot it as a network issue
Refresh your network connection. To do this, you can simply powercycle your modem.
Best if you could connect to a different network.