Windows 7: Blinking lines on screen.

I have been using my emachines netbook 350 for a year now and running windows7 in it since I bought. A month ago, I've started seeing those blinking horizontal lines on my screen. Almost half of my screen is affected. I wonder if it is a problem with my video card or just some viruses. Well when I print screen, the lines are not showing. The same as when I connect my netbook to a projector. Hope someone will help. Thanks!

If you have been seeing these lines for over a month then it would appear to have been happening when you had the video card driver problems just three weeks ago. See the thread here:
Emachine Netbook 350 Video Controller
It would appear that the previous problem was not solved then if you could see the black lines when you installed the new driver.
Were there black lines before the new OS was installed?
As you mentioned viruses, have you got an up to date anti virus software installed?