laptop screen

confused hi i have a acer laptop about 18months old. i started letting my son use it because i have a desk top too. i have noticed on the left side of the screen there is a strip running from the top almost down to the bottom of the screen that is a different colour. depending wot colour it is displaying at the time depends wot colour the strip is , and if you pinch the screen at the top where the strip starts it will go away. only to return when let go . the little man says he diddent do it but these things happen . any advice would be great. (except take it to a shop). cheers.