Error starting software usually has to do with missing or corrupt files. I would suggest uninstall 12 and 13 then reinstall 12 see if the program starts if not then I would call support, if it does reinstall 13. I don't think FileMaker charges for this type support.
Thank you for taking the time to answer. I did re-install 12 but with 13 still installed, no luck. I uninstalled 13, no luck. I will re-install 12 alone this time. If not, I will contact support as you suggested.