You might try rebooting the computer.  If that does not help, you could try installing it again.  Are you saying the Maximize square is not showing?  You might also try right clicking on the window header and them Maximize. 

 

When a program is shutdown the window settings are left at the last settings.  That's why some people have their Explorer windows change size from time to time.  They close the browser to find a pop up window behind the main window and when they close that window it will reset the window parameters for Explorer.