SOLVED! Skype failed to start or connect to server on Windows 10

After upgrading my Windows 7 to Windows 10, Skype failed to work or connect. Even after reinstalling with the latest Skype, it won't work with the following screen..."Sorry, we couldn't connect to Skype." Actually it is nothing to do with Internet connection...

To solve the problem, this is what I've done:

1. Start Task Manager (Windows Key+X, or right click on the time at bottom right corner), find "Skype". (Press "More details" if you cannot find the app)
2. Right click on "Skype" and select "Properties"
3. In the "Properties" of "Skype", go to the "Compatibility" tab.
4. Check the box "Run this program in compatibility mode for", and select "Windows 7" from the list.
5. Restart your Skype or restart your computer.