OK, ta for the screen grab..

I'd have blamed the graphics card and/or its drivers. I guess it's not that simple.

did you load the graphic drivers or update them when the anti virus was switched on?

normally you get black hex-tangles when you do that not the lines you posted so it might be worth doing another driver install with out the AV turn on

also I go with the other posters and say change you PSU and see what happens also

Mark

Yes Joe, she means a wooly jumper, as she is alluding to the fact that the "MAHOOSIVE fan" throws out a lot of cold air, which brings the overall temperature in the room down.