my monitor keeps going into power saving mode

[trimboy910]

So i recently bought two new Dell monitors. When I just use the computer normally it's fine but when I try to play video games after an hour or so it stops everything my monitor goes black and says power saving mode. it restarts the computer but the second monitor o cannot get to out of power saving mode. Plz help

Edit: I have not tried much of anything and second monitor is now working. I also had the problem before on just the first dell monitor alone. i don't think its heating problem because i (lol) tried putting a house fan on top pushing air and that time what i recall is it just turned the monitors into power saving mode

 

[ffg7]

onboard video or videocard? what wattage is your psu rated at as in 350, 400 watts or what?