Sometimes the display starts to flicker, and when it gets worse sometimes vertical lines starts to appear on the display, and when I shut down and then start the laptop again, it goes.
I had already given the laptop to the hp service center in the past but they returned the laptop doing nothing but updating the BIOS and resetting the factory installed OS, and the report said "The device passed all the tests, no problems found".
I myself carried out the tests by going in Diagnostics test (by pressing f2) but all the tests were passed and no failures were found , but the problem still exists.
I am uploading the images to give you an idea of what's going on.