Hi @jiahuing,
Has the laptop been dropped or gotten wet at all?
Try connecting an external monitor (TV?) to the laptop's HDMI port and check if there's a good display from the laptop showing on it.
Don't forget to press the Fn + F8 keys (both together) to change the display from the laptop screen to the external monitor.
If the display seen on the external monitor is OK then there's a problem with the LCD panel in the laptop.