Some users started experiencing Black Screen after installing KB4503327 Windows update released for Windows 10 October 2018 or Windows 10 Version 1809. If you are one of them experiencing this issue, then don't panic. This is just a bug, which Microsoft Officially confirmed and fix is already in works.
We are investigating reports that a small number of devices may startup to a black screen during the first logon after installing updates.
Microsoft says, this bug will cause black screen only when the first time system reboots and won't happen again on subsequent reboots. So, you don't need to worry even if you are experiencing this issue right now..Luckily, there was an easy fix that you can try and it will work for sure.
If you want to download KB4503327, then we recommend you not to do because of the above issue.
OK, lets see how to fix this black screen issue .
1) Press Ctrl, Alt and Del Keys simultaneously/together.
2) In the lower right corner,you will see power button click that, and select restart.
Wait for system to restart, and you can see the issue was fixed.