Line appears on screen for a split second, after turning it off the lines disappeared. Now they are back again and worse.

Only a few days after purchase my laptop started showing a thin, white, horizontal line across the screen. It would appear at random times (maybe every 3rd use on avg), but only lasting for a split second. It also seemed to appear on the same spot. I figured it was because my laptop wasn't turned off properly, so the cpu had been running for a while, and after turning it off the lines disappeared. Now they are back again and worse. They pop up more frequent and at differents levels of my screen. Sometimes black and sometimes white. I have no idea what to do and my warranty has run out.