I have a Dell U2711 connected by DVI to my Windows 8.1 PC with an NVIDIA GTX 760 card. If I leave the mouse and keyboard unused for about 5 minutes, the screen goes black. If I then wiggle the mouse the screen display reappears. My windows settings are for the display to never sleep, so I think it's something set in the monitor. Is this true? If so, how do I change the time limit and/or turn it off completely? Thanks, Jim