This seemed to work on Windows 8.1 (latest updates): disabling “Automatically detect settings” in the Network > Proxy control panel.
Not sure if this was just coincidence, or something else was fixed. Perhaps the new launcher is more sensitive to network issues / crappy proxy detection? I had previously tried basically everything everybody else had in this thread (repair, run as admin, disable firewall/av, uninstall/attempt to reinstall).
It’s a simple setting to test out, so it might be worth a shot.
YMMV.
More confirmation of this working. You can access the setting through Internet Explorer’s Internet Options or through the Control Panel as mentioned earlier by
RouterGeeks.6320.
Once I had unchecked “Automatically detect settings” I was able to start the install once again. Sadly I had uninstalled it while trying to fix the issue and now face the long download process again.
Thanks everyone!