Power Saving Mode

This usually only happens when I play games like Minecraft, Diablo, Skyrim, etc.. And it only happens randomly, I could go days without it ever happening and sometimes it just doesn't stop doing it. But the problem is I get a black screen and a sign pops up saying it's entering the Power Save Mode and then it just goes back to staying black. Another thing is if there's sound on when it does this, it just turns into a long beep for around 5-10 seconds or until I turn the computer tower off. And that seems to be the only solution I can think of, to turn the tower off then turn it back on. The computer is still on or at least I think it is because the white light to the power button is still on. I've tried buying new chords for it and I've tried updating everything I could think of and it still does it.