If you are using a PC, have you tried using System Restore to go back to a point before the initial failure?
You haven't even told you what platform you're on, Macintosh or Windows, let alone other details about your system.
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Thanks for all your help.
As I mentioned, I uninstalled and attempted to reinstall, but came up against Exit Code: 20. Apparently, I had entered the serial number slightly wrong--perhaps copying the colon when I copied it--and so, when I once again tried to install, I was more careful and succeeded.
That did the trick, reinstalling the program.
I'm sorry for not listing my specs. I'm on a Toshiba PC laptop running Windows 7. Again, thanks for springing into action for me!