Your video card or igp.
You changed the monitor did you also change the data cable?
I have a Samsung monitor that is 2 month old. It began having flickering pixels on the top 1/3 of the screen. We took it back to the store thinking the monitor was bad. We've turned the new monitor on, and after 15-20 minutes the flickering pixels have returned. It only occurs in the top 1/3 of the screen. So annoying, it is hard to read anything. Does anyone know what would cause this? Thanks.