A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Looks like an upgrade issue. I had 2010 pro installed when i installed 2013 pro. I uninstalled it after 2013 finished installing. I was worried my outlook settings might get messed with. Looks like that was the problem. I just ran the 2013 installer again and now excel files open properly. I was hoping that would fix my other annoying issue where clicking "enable editing" in word documents causes word to crash... but i suppose that's for another thread.
Advice to anyone with this issue or who is going to upgrade to 2013 - uninstall your current version of office first, or just re-install 2013. Worked for me, maybe it will work for you.