Re: Cannot find games following a hard drive change
@SierraLeone4 I can't be sure without seeing your computer, but what I suspect is that the registry entries for Sims 3 were wiped and not restored, and that's why the game has been showing as not installed even with all the program files present. If that's the case, then yes, you should be able to reinstall without any problems. The registry entries are what CCleaner and Revo are meant to remove, and leftover entries are what can prevent the game from launching after a reinstall.
Just to be safe though, please look at this guide to manually uninstalling and make sure you don't find any of the registry entries on the list.
https://sims3.crinrict.com/en/2011/01/tutorial-how-to-get-rid-of-unwanted-custom-content.html
It's a lot easier to remove them now than later. And to be honest, I'm not sure that your particular install would have exactly the same entries as a disc install, whcih is why I though it would be better to let CCleaner or Revo search. But you can look yourself for anything suspicious, especially anything with the name EA, Sims, or Origin in it. Since Sims 3 is a 32-bit app, you only have to look in the Wow6432Node section.