Power Saver mode when game starts/ends

[Platinum]

I use windowed mode, and sometimes when the game starts, my computer keeps reverting to power save mode and the screen goes black. I wiggle the mouse and it comes back, but then it goes back to sleep when i stop for a second. Then when the post game screen loads, it does the same thing. And, during the game when I alt-tab it does this as well. Not all the time, but its been doing it more frequently lately and no idea why.

[Melekor]

What is your setup - laptop/desktop, OS, video card etc?

Some things you could try:
-Update your graphics card drivers
-See if your video card or CPU is overheating
-Run with MaxFPS enabled, set to a low value like 30 or 60
-Disable power saving features in the control panel