Bebora1 I've split your post into its own thread since you're seeing a different issue than the (planned, limited) outage covered in the other thread.
Please remove the Downloads folder from Documents > Electronic Arts > The Sims 3, and download a fresh copy of one item you want to install. This will create a new Downloads folder, which is fine. The point is to keep the launcher from loading all the other files in Downloads at the same time. These files are also redundant once you've installed their content.
If that doesn't help, then as a test, remove the DCCache folder from the Sims 3 folder as well. This will remove the Store and custom content you've installed through the launcher, but that's the point, to see how the launcher behaves with none of that content. You can put back the original DCCache folder to restore that content, but please don't do that until you've tested installing a new item.
As a side note, if you're installing sims, households, or lots, and you don't need any cc that might be attached to them, let me know.