Graphics Artifacting

I have an AW 17 with Core i7-4910MQ and GTX 880m setup that's plugged in to an external monitor via HDMI that I use for gaming, running the latest bios (A14) and drivers. I left Starcraft 2 running overnight the other day by mistake, and when I woke up in the morning there was a lot of pixel artifacting and lines on the monitor side (but not on my laptop screen). I initially suspected dead pixels on the monitor (since it's from '08), but the pixels which are artifacting changes depending on what's being displayed, so I've concluded that it's not the monitor.

I also noticed that it struggled more when trying to render heavy 3D images, such as actually going in-game versus my desktop, and at times refused to render and had a flickering black screen instead. So my next suspicion was that the VRAM on my GTX 880m was damaged from overheating or some such (which would be the perfect excuse to upgrade to a GTX 980m haha), but when I disconnect the monitor and run games on my laptop screen, there is no artifacting at all, which leaves me thoroughly confused as to what the issue is. Anyone have any thoughts? Pictures are below of the artifacting.

Update:
I continued to run Starcraft 2 a bit more, and everything suddenly returned to normal after I unplugged and replugged it back in. Now I'm suspecting that everything had been running on the integrated Intel HD GPU, which would be damaged. I'm theorizing that everything returned to normal once the GTX 880m kicked in.

 

Could be the cable you using to connect to external monitor. Try another to see if problem continues.

Good luck.

 

Replaced the cable - still no dice. The other thing that I would suspect might be the HDMI port itself...

 

is it fine with the built-in display?

 

Yes. Built-in display runs fine. I don't have a second monitor here to test, either. I might pick up an HDMI to mini-DP converter just to check if it's the port.