I have dual monitors that work perfectly at windows startup. After leaving the computer alone for sometime (after powersave has occured on the monitors), I arrive back to the pc to find only one monitor returns from powersave (the same monitor everytime) Rebooting the system corrects the problem; or entering the device manager and selecting "scan for hardware changes" will also correct the problem. I've updated the video card to the most current drivers possible and do not know where to go after that. It's very annoying and have the exact same thing happening with a PC at work with completely different hardware. I'd love to get to the bottom of this.
Please complete your system specs, or at least provide details as to your motherboard, CPU and video card.
We should be able to help you better if we know your hardware.
My Computer
At a glance
Windows 7 Pro x64 (1), Win7 Pro X64 (2)i5-3350p 3.1Ghz/6MB-cache (1); E8400 3.0Ghz/6...8GB PC3-12800 DDR3 (1); 4GB PC3-10600 DDR3 (2)ATI HD7750 (1), (see TV cards); ATI R7 250 (2)