You can go to the power options and change the power plan you have to what you want.
When a Pc goes into the power saving mode the screen will go black because in the power plan there is a setting for it to shut the display off after so many minuites being idle. There are a lot of options that you can change or adjust in the power saving plan page.
Control panel > System and Security > Power Options and if you want a detailed selection you can select the advanced button. In the advanced page each line has an option or several options.