@dipensejpal first you need to determine if this is related to your display or the motherboard. Connect an external monitor and see if those squares disappear. If so, you know it is your display. If not you know that the error is on your motherboard. Sometimes dust/debris or a loose cable can be the cause of this, other times it is a bad component (VRAM) in the video circuitry of your laptop.
Start by checking the display first.