Users have reported that there are serious reliability issues with Microsoft Windows updates KB4480970 and KB4480963 which rolled out to users on Jan 8th 2019 (see links below). If you can't connect to your machine and are being repeatedly prompted for your Windows Credentials, then you may be affected by the bad update.
Updated Jan 14th: To fix this please install Microsoft's KB4487345 follow-up update on the affected machine from here: https://www.catalog.update.microsoft.com/Search.aspx?q=KB4487345 . After you install the update, reboot the machine and you should be able to connect properly from that point onwards.
More information about the bad update: