Ok I just started using Office 2013 and excel 2013. My issue is that when I am on one tab and want to say do a sum formula using cells on a different tab when I type in Sum( and go to the other tab to select the cells the little green box that shows what cell you have highlighted is gone! I have no idea how this happens but it's really annoying and I can't seem to figure out if it's a settings issue or just an issue with excel 2013. Please HELP!