Hi @lk1991 ,
Try connecting an external monitor to the laptop and check what the display is like on it. You can either connect using the vga port or the HDMI port. (even a TV can be used as an external monitor if you have the appropriate HDMI cable to connect the two together)
Don’t forget to press the external monitor action key (usually 4th key from the left, top row with rectangle symbol with line either side) to toggle between the laptop screen only, the external monitor only or both screens on together.
If the external monitor’s display is OK then there is a problem with either the laptop’s LCD panel, the LVDS cable between the motherboard and the LCD panel or the LVDS cable connections (at either end).
If the same problems are being seen on the external monitor then there is a motherboard problem
What is the model number of the laptop as shown on the information label on the bottom of the laptop?
If you determine that the problem is in the laptop screen or cable etc, then search online for HP Pavilion (insert full model number) manual to find the HP support page for the manual. Once there click on Manuals to find the maintenance and service guide.
The guide details all the necessary steps and procedures to replace all the major components in the laptop. It also has the spare part numbers as well. For example if the LCD panel is faulty then search online only using the part number appropriate to your particular model LCD panel, to find suppliers of the part that suits you.