Hello there. I'll try to give as clear and accurate a description of the problem I'm experiencing as I can.

I've been enjoying playing with The Sims 3 for a couple of months now. I got it as a digital download from Origin, and liked the base game so much I added the Late Night, Generations and University Life EPs. (All paid for and above board.)

I'm using a MacBook Pro from early 2011, with 16GB memory, 2.2 GHz Intel Core i7 processor, AMD Radeon HD 6750M 1024 MB graphics card, and running OS X Yosemite 10.10.1. It generally runs without any difficulty.

I began to experience an increasing number of glitches and crashes in my games, so I followed Bluebellflora's guide to doing a clean uninstall and reinstall, which has worked for me in the past. I'm really sure I removed all the leftover files that might taint a new installation. But after reinstalling the base game, patching it to the latest update, adding Late Night and Generations again (I don't want to play with University Life at the moment) and trying to open the game, only a couple of seconds after clicking on its icon I get the message "Unknown error occurred." The game simply won't start; I can't even get the Launcher on screen. This didn't happen any of the other times I uninstalled and reinstalled. I even downloaded a whole new copy of the game in case the installer .dmg I'd saved as a backup was somehow corrupt, to no avail.

After reading some troubleshooting articles and threads, I thought the problem might be a lack of free memory, but I've run Memory Clean and got it to more than 10 GB of free memory available, so that seems unlikely. I've also repaired my disk permissions.

Although I've used custom content and mods like the NRaas suite in the past, there are none in the new installation's Documents>Electronic Arts>The Sims 3 folder, either .packages or .sims3packs, so I don't think they can be causing the problem.

The one bright spot is that I backed up my favourite families' games before uninstalling, so they're safe and sound waiting for me to get back to them. But how can I when the game won't open? I hope someone here can help me. This is awfully frustrating.

Edited to add: I have also tried bypassing the Launcher, but got this message: Service initialization failed (0x0175dcbb). I tried Googling that code but was confused by what I found, particularly since the "solution" that seemed to have worked best involved the use of cracks. Can anyone advise?

Edited to further add: Here's what I've tried since then.

1. Full, clean uninstall of all Sims and Origin-related files, as per BluebellFlora.
2. Restarted computer.
3. Ran Memory Clean, repaired disk permissions.
4. Downloaded and installed Origin client.
5. Downloaded new copy of base game, using the little "i." This took several hours, because, well, New Zealand.
6. Installed base game (by clicking the "Install" button in Origin).
7. Downloaded manual superpatch, extracted it and ran it. It did its thing.
8. Repaired disk permissions and ran Memory Clean again just to be on the safe side. Got it down to 12 and a half gigs free memory available.
9. Tried to open The Sims 3, using the Play button in Origin. Plumbob appeared in dock, but didn't bounce, and a couple of seconds later, "unknown error occurred."
10. Tried to open The Sims 3 from Launchpad. Exactly the same. Used "sudo purge" in Terminal and tried again. Exactly the same.
11. Despair?