@MsV0912 When a town doesn't load, that means the pack isn't loading, but it was clearly installed correctly the first itme around. The most obvious culprit would be the pack selector in the launcher (the tab is called "extra content" or something like that). Packs can frequently uncheck themselves when you're not looking, and sometimes they look like they're checked but still don't load properly. Some players have taken to unchecking and rechecking all the boxes each time they load the game, just to make sure everything loads.
The specs EA lists for TS3 haven't changed since the game was released, which means they're the specs to run the unpatched base game. Even without packs, the base game has many more features than it did in 2009. When recommending a computer to run all packs on high settings, we recommend these specs:
2.4 GHz processor, i7 for a laptop (i5 is fine for a desktop), or AMD equivalent. Not U- or Y-series.
6 GB RAM, though 8 GB is better
Nvidia 950 or 1050 in a desktop, or 960m or 1050 ti in a laptop, or AMD equivalent
hard drive with at lesat 512 GB total storage, to hold program files, saved games, and custom content
If you're only going to run Late Night (and High-End Loft Stuff. which adds almost nothing to the game's demands), you wouldn't need such strong components. I'd expect a 2.0 GHz processor, again not U- or Y-series, to be fine. 4 GB memory might be as well, although it would be tight; you'd want to close all other apps and play while offline. A weaker dedicated graphics card would struggle very much with Pets, Seasons, Into the Future, and Island Paradise, but Late Night wouldn't present any issues. Integrated cards may or may not handle LN, depending on their strength.
As for storage, the key is that you can keep at least 35-40 GB free at all times. The game's program files will take about 10 GB, but the size of your game folder, with your saves and installed content, could be much larger. Still, it's the easiest issue to manage, since you could store other data on an external drive if you really needed to.
You could always post a dxdiag on the other available computer if you want an idea of how TS3 would run. And you can install on as many computers as you want, without uninstalling on this one. Since you run the game through Origin, you can only play on one at a time, but Origin doesn't care how many installs you have.