So I got this issue: sometimes, random when I'm in-game, the screen goes gray and a messagge saying "Energy saving mode activating" pops up. The computer shuts down, like a stand by shut down, and I've to hit any button to restart it. It's pretty anoying.

I've tried both HDMI and DVI cable and it's the same.
I've check the temp and they're all right.

I got a LG IPS234V-PN and a Zotac GTX 660 with updated drivers.

Any solution?

I don't think that a monitor can shoutdown a computer. Have you installed some software?

Maybe is the monitor that turn off itself, not the computer. Try to go on your LG: press the func button, right, disable/enable super energy saving.

I've checked on the monitor and it's turned off.

Also, W7 hibernate and stand-by after time are off.