The Sims 3 will not launch through Steam

@victorlemorte  The launcher running in the tray issue doesn't normally prevent TS3 from opening at all, although it can be annoying.  (It's easy enough to fix, but there's no point until the game is actually working.)  First, please make sure that .NET framework 3.5 is enabled on your computer.  Hit Windows key-R and type "appwiz.cpl" without quotes into the box, and enter.  In the File Explorer window that appears, click "Turn Windows features on and off," and you'll see this:

The .NET frameworks are in the first red box, and your configuration should look like it does in the screenshot.

If this isn't the issue, try temporarily disabling your antivirus/firewall, just long enough to test.  If that's the issue, you can set an exception for TS3W.exe (with the W), and perhaps Sims3LauncherW.exe as well, although the second one usually isn't necessary.

If that doesn't work either, try launching the game while completely disconnected from the internet, as in, turn off wifi and/or pull the ethernet cable.  You shouldn't need to be signed into Steam—just launch directly from TS3W.exe inside the game's program files.  The path should look something like this:

Program Files (x86)\Steam\steamapps\common\The Sims 3\Game\Bin

If none of this helps, please run a dxdiag and attach the results to a post here.  It will cover not only hardware but things like drivers and disc space, as well as list the last 10 Windows errors, hopefully with some information about why TS3 didn't launch.

https://help.ea.com/en-us/help/pc/how-to-gather-dxdiag-information/