Crashing when you press A to start the game?
I have a probable solution for you if you do not mind starting with a new save. I have the same problem but have been waiting for official support (Ticket ID #42186) because I am not very excited to start the game over again with a new save. Basically, you reset the game offline, play a bit to create a new save, turn internet back on, and start the game again:
1. Disable internet on computer. Unplug cable, disconnect wireless, disable adapters, whatever you need to do.
2. Reset the game. Ctrl+i -> Apps-> Forza 4-> Advanced Options-> scroll down a bit, click Reset button
3. Still with no internet, start Forza 4 normally and dismiss the numbered error message
4. For me, the game starts in offline mode with a new save. Right from the very beginning of game.
5. Play for a while and run a couple races. You deserve it. You've been without FH4 for a while. I did like 5+ races.
6. Quit the game and re-enable your internet.
7. Start Forza 4.
8. Choose your new, local save over the old, cloud based one. WARNING: This likely overwrites old save**
9. Play the game online with your new save.
** For step 8, you can select "Choose next time" at the bottom of window to play online without overwriting your old cloud save. This is the option I took. I can confirm that I was presented with the same choice of selecting which save to use the next time I started the game.
Do not expect a quick resolution by entering a ticket. I have had one open for 4 days without an update from the support team. This is with me providing the above details about how I can get my game to work, basically showing that the save in the cloud is corrupted somehow. I just want to know if my old save can be rolled back or recovered and a timetable of when that may be. This way I can decide if it is worth it to wait for official assistance or resolve the issue myself. Ticket ID #42186
I also found the below quote in another thread titled "Crashed the game after falling through map, now I can't get back in." This is after I had already came to the same conclusion above:
Originally Posted by: CTPAX90 
That what I got as an answer few days ago
Hello,
Can you please try the following things and try to sync your save after each one.
Please restart your PC then load your game to sync data.
Please try to manually update the game and any DLC using the Microsoft Store.
UWP Reset Application
Windows>Settings>Applications>title>Advanced Options>Reset
Follow the steps in this article.
https://support.forzamot...nd-Resuming-Windows-10-
Uninstall then reinstall the game and any DLC.
If you get the Invalid Profile error message after the above steps you may need the delete your save as it has become corrupted. To fix this issue please follow these steps based on your device. If you have to reset your save please let us know so we can provide compensation.
PC
1) Make sure your PC Offline Permissions is set to ON
Open the Microsoft store.
Click on your profile Image and then click settings.
Make sure your Offline Permissions is set to ON
2) Start the game, wait for the start screen.
3) Disconnect your PC from the internet.
4) Go to your Windows 10 Settings --> Storage --> Apps & games -->Forza Horizon 4 -->Advanced Options -->Select the "Reset" button.
5) Start playing for a few minutes to create a new local save
6) Connect back to the internet.
Thanks.
If the above is legit, then this may end up being a similar answer that most of us get for this issue. It will stink to lose all my progress, but if this is the ultimate answer, please let us know. Why have the customer wait this long to move on and continue to enjoy your game? Apparently I found the same resolution on my own, please just confirm whether I am losing my save or not and we can move on. Ticket ID #42186