Display problems

[Sun_rays]

Hi. I have a Hp laptop probook 4540s.It was working fine until last couple of days. Last week it started giving a horizontal white dot line on the very top of screen( like this ............. in white) for the entire width of the screen.It appears every 2 or 3 sec and it will also shake sometimes which makes letters difficult to read. 

The problem exists everywhere,even in boot screen. In short when I press power button and screen start displaying same problem also starts. 

Today I connected an external lcd monitor via vga cable and it works fine. No line and no flickering. What could be the problem?? Could it be just loose contact or something in laptop screen cable?

[WAWood]

@Sun_rays 

Screen artifacts like this are due to video chip failures and/or screen hardware failures.  By connecting an external monitor, you determined it is not a video chip failure -- but the screen hardware itself.

That would require the screen to be replaced and that is neither a simple thing to do nor cheap.

We are not able, or permitted, to provide any repair estimates or equipment prices.

For this information, you would need to contact an HP Repair or Service Center.

If you live in the U.S., here is a link to the HP Service Repair Centers:
https://www.service-center-locator.com/hp-hewlett-packard/hp-hewlett-packard-service-center.htm

If you live outside the U.S., here is a link to HP Service Centers, by Country/Region: https://support.hp.com/in-en/service-center

Good Luck