Have a user running Windows 7. Had office 2010 installed. Just upgraded to office 2013. When opening a single excel file it can be closed no problem. As soon as he opens 2 excel files then he cannot close excel. Hitting the X does nothing. Only option is to end task which then closes all open excel files. If I open Excel using excel /safe then it all works fine. I disabled all add ins but still same issue. Did a repair of excel but make no difference.