Broken Graphics card?

Okay so i bought a new motherboard and CPU (sabertooth p67 and i5 -2500k) and SOMETHING is faulty.

My current build:


Tri-screens
i5 - 2500k
Scythe Rasetsu (cooler)
Sabertooth p67
Radeon HD 5670
4GB of 1333mhz RAM
Corsair TX750
Coolermaster 690 ii
1TB HDD

What happened originally was occationally my screen would freeze (apart from my cursor which could move.. but do nothing) and them would black out and come back 5 seconds later with a message "AMD display driver has stopped responding and has successfully recovered". But by the time ive read that message the screen has frozen and it has happened again. It will keep happening untill eventually it will stop and a dialog box will pop up saying "displayport link failure. Your display port cannot output the resoloution / refresh rate of the monitor, check the cable is firmly attached" however even when i try completely disconecting the display port monitor and working on two screens the same situation.

This doesnt happen when playing games, howver just randomly. It happens most when i am playing a game and then start doing something on another screen (facebook or something). Or when i am browsing the internet. Dont recall it ever doing it when i was just playing a game.

Occationally the screen lags too. I have reinstalled drivers, updated to latest chipset / bios and reinstalled windows.

I have googled this problem and have tried EVERY soloution but none has worked. However now i am getting strange lines across the screen randomly and i was just playing a game and suddenly i was littered with visual bugs. I had green lines shooting diagonally as if it were a disco and triangles in random places. I also had text across the screen. While writing this message internet explorer keeps bulging randomly and jolting.

I have monitored tempratures and neither my graphics card OR CPU are overclocked. the voltage imput by my 750 watt power supply is all fine and 750 is more than enough to power my rig. the 5670 doesn even require a 6pin PCI connector.

so my question, do i need a new graphics card or is it possible its my mobo / cpu / RAM (even though when stress testing it never crashes however when i do stress test with prime i always get a rounding error 1 hour / 2 hours in, i have increased voltages yet ALWAYS get a rounding error)

thanks