David, the good news is you're not stupid.
The bad news is that you can't buy Fences 3 anymore. Stardock has stopped selling Fences 3 and now sells Fences 4 only. If you saved your installer for Fences 3, use it to reinstall. If you didn't save it...it's gone.
You should also upgrade to Windows 11 as Microsoft ended mainstream support for Windows 8.1 on 1/9/18, and will end extended support on 1/10/23 so if you aren't already vulnerable to attack, you will be in a few months.