Have you tried changing the Power options in “Advanced” settings tab? If not please try the below mentioned steps:
Click Start button, click Control Panel, click System and Security, and then click Power Options.
On the Select a power plan page, click Change plan settings for the plan that you want to change.
On the Change settings for the plan page, click Change advanced power settings.
On the Advance settings tab, expand Sleep, expand Allow Hybrid Sleep, and choose OFF.
On the Advanced settings tab, expand Sleep, expand Allow wake timers, choose Disable for both when your computer is running on battery and when it's plugged in, and then click OK.
On the Advanced settings tab, expand USB settings, under USB settings expand USB selective suspend settings, choose Disable.
Click Apply and then OK to save the changes.
Check if the above steps work. If all those settings are fine and still the issue persists, this could be malfunction of OS. In such case, performing a Windows Update could help fixing the issue.