Click Save changes to bring the sleep option back.Make sure to check the Sleep box down below.Next, click Change settings that are currently unavailable.In the left pane, click Choose what the power buttons do.In the next window, click Power Options.When the Control Panel window has opened, go to the drop-down list next to View by.On your keyboard, ssthe Win + R key combo to launch Run.This fix is available for all versions of Windows 10 and is not as complicated as it may seem.
Option one: enable sleep mode via Control Panel
If you are still facing the issue follow the next method of using registry editor.