To change this, do the following:
1) Navigate to the Control Panel by clicking Start and then
Control Panel. Then double click on
Power Options as shown below circled in red.
2) This will then display the Power Options window as shown below.
3) Once you have opened the Power Option Properties, under
Power Schemes select the one that best suits your PC system.
4) Then you can select whether or not to switch off your monitor and/or hard drives after a period of time when it is not being used.