GummyMeister

Lay a pillow under the laptops head and call 911.
 
In all seriousness we are going to need far more detail to even have hope with helping you. The screen can flicker due to a plethora of issues. First thing I would do is make sure you have your drivers updated. The next thing I would do if this doesn’t resolve the issue is verify that you didn’t route any ribbon cables wrong (or break them) that connect the screen to motherboard.

what this guy said...
 
i would check that you did not damage the internal display cable when you opened it