its not if its configured for excel its how its configured windows sends a command to the excel program when opening files that tells excel how to handle the file some times the commands get messed up by other programs but it sounds like it may be the antivirus you use, and as far as reinstalling you may be able to see if there is an option to repair the program.
try this instead of opening the file try dragging the icon for the file into the icon for excel, does it still open slowly?