Flickering horizontal lines

[Apps]

What youve described is called Horizontal line artifacts. I believe. If it is this, then your videocard is having trouble with the horizontal snyc.

Typically, this occurs when the video card overheats. Information can not get in sync with the card and feedback.

Unfortunately, the only remedy for this is to turn down your video settings, until its gone. Past that, you simply need to purchase a new video card.

Here is a picture of an example.