This video will show you how to fix this issue in Windows 10: you try to launch Forza Horizon 3 and/or Forza Horizon 4; you receive the small window splash screen with the game title and showing a still image of an exotic car (this all before the actual opening credits and loading screens), and then after a few seconds to a minute later of waiting, the small window splash screen disappears (shuts down) and your game never starts (nothing else happens). This issue was noted on my end after applying the Windows Update following March 12, 2019. The fix is quite simple: right-click on the Windows 10 clock found in the lower right of the desktop screen (in the taskbar system tray) and then select Adjust date/time. Under the subsequent Date & Time menu, switch Set time automatically to ON. Once done, close the Date & Time menu and then re-launch Forza Horizon 3 or Forza Horizon 4 - your game should once again boot as intended (problem solved).
