I had this same problem on 2 different computers, both Dell 660, read all the forums, lots of people with the same problem tech solutions rarely fixed anybodies problem including mine. Monitor Acer touchscreen windows 8, connected with HDMI and USB. While both of these are connected add the VGA cable and power up computer, VGA will open the monitor (primary connection ), I then pressed adjust screen resolution ( not sure if this step is required ) then noticed I had touchscreen capabilities again. Unplugged the VGA connector and monitor stayed on. Rebooted computer everything worked correctly. Then went to control panel in PC settings and turned off sleep mode for computer and monitor, one I think good idea I got from tech thoughts of causing the problem.