sounds like faulty screen
2 reasons
1 - faulty - new screen
2 - loose connection - if you are confident enough it's not too complicated
there are usually a mix of screws (often hidden behind sticky blanks or rubber pads - use point of knife to carefully remove (blood is not good in lappy - so gently gently)
then the case normally clips together ... so you have to feel for the fixings .. and unclip
however first you should update the video driver ... it's unlikely but worth a punt before you reach for screwdriver