What is happening ? Not at all starting ? Or any other behaviour ? (do you see the menu ?) Can you please attach your logs ? (you can find them under My Documents\assetto corsa\logs.
I recently upgraded from Win 8.1, 64-bit; to Win 10; 64-bit. I open Steam and click on Assetto Corsa. Then I click Play Game. I get a brief black dialog box that I think says Launching Game; then nothing. One thing to note - I do not seem to have received an Activation Code for this game. Another thing to note - my Grid Autosport no longer runs; I keep getting the Play Grid Autosport dialog box over and over. Launcher Log: 8/9/2015 10:50:30 AM Skipped MoveUGC PID: 1104 AC Launcher ver. 0.15.730.4719 Running on: Microsoft Windows NT 6.2.9200.0 Searching for .config at: AssettoCorsa.exe -> C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\AssettoCorsa.exe.Config Current Culture: en-US / en-US Length:1 assembly loading: Steamworks.NET.dll Loading C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\launcher\support\Steamworks.NET.dll assembly loading: CEF3.dll Loading C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\launcher\support\CEF3.dll Initializing Steam: True. Steam ID: 76561198232496288 assembly loading: AC.CEF3.dll Loading C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\launcher\support\AC.CEF3.dll OnBeforeCommandLineProcessing - switches: 16 - args: 0 bwsi disable-cast disable-d3d11 disable-dhcp-wpad disable-extensions force-device-scale-factor=1 js-flags="--expose-gc" lang=en-US log-file=J:\Documents\Assetto Corsa\logs\launcher_debug.log log-severity=info no-proxy-server no-sandbox remote-debugging-port=30150 single-process user-agent=Assetto Corsa Launcher winhttp-proxy-resolver Cefsettings: App Language set to: App Language set to: en Locale Dictionary Initialized App exitcode: -1 Hardware acceleration: True App Language set to: Launcher_Debug.Log: (empty file)
Meanwhile, here is a list of programs identified as "problematic" with steam https://support.steampowered.com/kb_article.php?ref=9828-SFLZ-9289
Strange, can't see too much. Launcher stops after init sequence, and debug is empty.. Do you have any themes installed for the launcher ? Have you made a Steam Integrity Check ? Do you have the latest DirectX installed ? Do you have the Microsoft Visual C++ libraries installed ? If all this fails, maybe it's better to ask for help on official forums, running out of ideas..