Excel won't force quit and won't open.

I'm on Yosemite. No problems at first. But now if I try to open an excel file I get the error message "The application “Microsoft Excel” is not open anymore." I get the same message when I try to open the application from the applications folder. Excel appears in the Force Quit options but won't disappear when I force quit it. That's about the limit of my troubleshooting, any ideas?