Game hangs on loading

Problem

My game hangs on the initial loading screen and it takes forever to load.

Large save games with lots of downloads can take a while to load.
This issue can be caused by a faulty or outdated custom content or mods.
Computer doesn’t fulfill minimum requirements
This issue occurs if you have an active connection and files in the Tray folder (your houses and Sims).
Patch 1.21 had an issue that a large amount of screenshots freeze the game.

Remove incompatible mods and delete your cache files. Use the 50/50 method to find the any outdated or corrupted mods
Make sure your computer fulfills the minimum requirements.
Merge your custom content using S4Studio.
Put Origin in offline mode to start the game and only go online, if you really need the gallery.
A lof of files in the user folder have been proven to be an issue in the past. If your loading screens start to get longer, check the folders and move unneeded files (screenshots, videos, Library Sims and houses, music, not played saves games, ..) to a different location on your hard drive.
[MAC] Endless loading screen when trying to load a savegame (Patch 1.68.156)

Credits

Many users who helped figure this out