Windows can be incredibly stupid in the way it handles multiple displays. You would think that if you only have one display connected to all your various ports, then that is the one it would use! But it is not always so!
Is there any way you can connect a 2nd monitor to your onboard vga/hdmi port, so that you can configure it to turn it off? Or maybe you can turn off your onboard (integrated) video in the bios. I would try the bios option first. Most likely what happened is that when you upgraded your memory, somehow the bios settings reverted back to default settings. This would have enabled the integrated gpu, whilst windows still thinks you're using the discrete. Leading to a level of confusion that these two billion dollar companies simply could not, and probably never will figure out.
I am looking for a cheap upgrade to my 3 year old computer.
AT forum member #1: Buy a 4790k
I am looking for a way to get 10 more fps in TF2.
AT forum member #2: Buy a 4790k