Computer randomly freezing after installing new monitors

Hello,

I recently upgraded my monitors to LG IPS237L x2 (resolution 1920x1080) and at the same day upgraded to Windows 8 (after the computer had first started freezing up). Before this I had two very old monitors (I think 17", resolution was 1024x768). I was afraid that my computer couldn't handle this much of an increase, and I think I was right, but I'm not quite sure what the problem is. My computer specs are as follows:

Windows 8 Pro 64-bits
Processor: AMD Phenom II X6 1055T 2.80 GHz, 8 GB RAM
Graphics Card: NVIDIA GeForce GTX 460 SE
Power Supply: MS-Tech ATX Power Supply 750W

Before buying the new monitors my computer occasionally (once every few months or so) just instantly powered down for no reason (was not confined to playing games), after which I could just restart immediately and there would be no problems. Also, sometimes (usually once a month too) my screen would go black for a couple of seconds, then come back displaying the error 'Display driver stopped responding and has recovered'. This only happens when gaming. Since these issues didn't have a serious impact on my computer's life I never bothered to follow up on it.

But ever since plugging in my new monitors, my computer tends to just freeze for no reason (monitors instantly go black). This happened several times a day so far, even when I'm not playing any game. After a minute or so my computer automatically restarts. When I still had Windows 7 it would display an error (after the restart) that said I had a BlueScreen, but no such error appears on Windows 8. Peculiar thing, last night during my raid the freeze happened twice right when I accidentally bumped my knee to my computer. After installing Windows 8 I still encountered the 'Display driver stopped responding and has recovered' error once. I always keep all drivers up to date (or try to, at least  )

I would like to know what piece of hardware is probably the cause of these malfunctions (as I did a clean install of Windows 8, it can't be software related). I have enough budget to upgrade, but I wouldn't like to just throw money at my computer and finding out that the problem still won't be fixed.

Thanks in advance!