Everytime I start my MacBook Air there is a blank interface window When I start my MacBook Air, an empty/blank window appears. Does anybody know how to get rid of or repair it so that when I boot up it doesn´t appear? There is nothing else wrong with it, I can just close the empty window and everything is fine.
I have solved the problem by reinstalling latest OS. Follow these steps to do it :


Shut down your Mac first
Restart and keep cmd+R buttons pressed until Apple Logo shown
Choose from the menu reinstall OS (in my case : Reinstall Sierra)
Follow on screen instructions.


Reinstalling latest OS doesn't change or delete your current settings or installed softwares.