Sims 3 Crashing/Closing At Startup

@AMorbidVisionary  I'm glad to hear the clean folder worked.  You can now start moving your content from the old Sims 3 folder to the new one and testing.  Where the game has created new files or folders, it's best to use those rather than recycling your old ones, for example leave the new Saves and Library folders where they are and just add the contents of the old ones.  And don't move over anything that's been recreated.  Here's a description of all the files in your user folder so you know what you might want to keep:

https://sims3.crinrict.com/en/2011/01/faq-user-files.html

Make sure to test everything you move over so you know immediately if you're reintroducing the problem.  You can do so in batches, especially with content that's unlikely to be the issue, like your saves.  But be careful with mods and custom content—the tools to detect bad cc and outdated mods are useful but somewhat limited, so you'll still need to test yourself.

The store that upgraded your laptop should have found compatible RAM, so don't worry about that for now.