I just bought Forza Horizon 3 and CAN'T PLAY IT. Same issue as everyone here. I also just made sure my only microsoft account is verfied in Windows 10 but that doesn't do anything for me, the best part is that I could play the Forza Horizon 3 Demo without end a few months prior, without any issue at all!
The "fix" of downloading some random game from the store and then starting Forza Horizon 3 doesn't work for me at all. My graphics drivers are up to date, my specs are:
GTX 1070 TI
i7 8700K
16GB DDR4 RAM at 3200MHz
2 SSD, 1 HDD (all from different manufacturers)
I also tried the move trick to every disc it didn't help at all, I also reinstalled and fully downloaded the 55gb three times now without anything getting better. The best I could see was the loading ring for just about one second and the text, just once before crashing, I couldn't even replicate this horrible state. NOTHING WORKS. I now come to understand why Amazon is having so many 1 star reviews with everyone and their mother complaining about this, fix your game Microsoft this is an insult to your customers!
EVERY other game I have played on my PC works perfectly fine, be it new or old, everything works fine, 20 games in total that I have played, installed and enjoyed within the last couple of months I have this PC in this very configuration.
*I'm now downloading the Forza DEMO again to see if that starts, it would be insane if it did but I have a feeling it will...