Try connecting an external monitor and check its' display.
If the external monitor's display is also not steady then there may be a problem with the motherboard or the GPU or possibly with the graphics drivers. Try starting the laptop in 'safe mode' to see what the screen does.
If the external monitor's display is steady then there may be a problem with the video flex cable between the motherboard and the screen, with the video flex cable connections at either end (motherboard or screen) or with the screen itself.
Here is a link to a video which shows how to disassemble the laptop to gain access to the cable and the LCD screen.
As with all electronic devices be careful when dis-assembling, with most there is no need to use force to disconnect things. Be gentle, you don't wish to cause more problems than you had before you started. If things aren't going as you think they should, STOP, take a break and think it through and then start again. This forum has a lot of questions from people who got frustrated and damaged their equipment. This is not to put you off, far from it.
Hopefully this is of some help.