Laptop - Macbook Pro Retina?
If so, you can try this (I do not guarantee it will work for you, just a possible solution for some macs):
http://www.appstorechronicle.com/2012/10/retina-macbook-pro-screen-flicker-solution.html
Other issues that cause flickering:
loose video cable
screen or lid assembly itself received some kind of damage or was hit hard enough to cause the issue.
All else fails, you may have to take it to a repair shop that can fix Macs .or an Apple Store