https://serverfault.com/questions/625332/windows-update-not-working-on-windows-2012-r2-standard

1. Stop the Windows Update service.
2. net stop wuauserv
3. Delete the Windows Update cache directory C:\Windows\SoftwareDistribution.
4. Remove-Item -Recurse -Force C:\Windows\SoftwareDistribution
5. Restart the computer. (On one machine it required several restarts to actually get everything deleted from this directory, so keep trying if necessary.)
6. Run Windows Update manually again. It will fail almost instantly and offer to run a diagnostic tool. Download the tool and allow it to run.
7. The tool will find and fix some problems. At this point, run Windows Update manually again. Windows Update worked fine at this point.

Take these steps to reliably fix troublesome Windows Updates:

1. Turn off automatic updating
   • Control Panel → Windows Updates → Change Settings → Never Check…
2. Reboot
3. Search the Internet for “Windows XX latest update client”
   • Where XX is your Windows version
4. Download and install the latest update client for your version of Windows
5. Install Windows Updates