Dell L502X Display Horizontal lines

[Binoy]

My laptop is Dell L502X. I get horizontal lines on my screen sometimes when I am using it.When the horizontal lines are seen on my laptop screen , when I press the edges of the screen they stop appearing and the screen appears normal. What can be the problem ? Any help is appreciated. Also I tried connecting laptop to external monitor and found no such issues.
Thank You
B

 

[Tmagic650]

The internal video chip may be over-heating or the video cable between the motherboard and the LCD display is damaged...

 

[Binoy]

Well can it be video chip since it works fine on external screen.

 

[Tmagic650]

No I guess not, just the video cable or display panel