Half of my laptop screen shows greenish colour

Solution 1:

Last chance to avoid repair:

Boot on a Linux LiveCD or USB key. If the display is fine, you have a driver or other software problem.

Try with an external monitor on the HDMI/DisplayPort/VGA port. If the display is also half green it's either software or a hardware issue on the mobo (which would be extremely weird).

Now, if the red signal was broken in the motherboard-to-LCD cable, the display would be completely green, not just partially. Thus the cable is fine. The motherboard is probably fine too.

Most likely one of the row driver chips in the LCD is busted, and you will need a replacement LCD, or a technician skilled enough to replace the LCD control board.