After a specified period of time Windows 10 will put the monitor to sleep, so the display will go black and you will need to re-enter your userid and password to get access to the system again. This behavior can be changed either via a graphical user interface (GUI) or by using the command line utility
powercfg. For the GUI method, right-click on the desktop and select Display Settings then click on Power & Sleep and then change the value for "When plugged in, PC goes to sleep after". For the command line method, from a command prompt enter the command
powercfg -change -monitor-timeout-ac xwhere x is the timeout value in minutes. E.g, for a timeout value of one hour, you could use
powercfg -change -monitor-timeout-ac 60. If you use zero for x, that is the same as setting the value to "Never" via the GUI method.