I'm having the same problem right now. The game installed and launched fine but in the meantime the game won't launch anymore (not crashing when starting a race - that's a different problem).
Launching the game with the link "Launch MX vs. ATV Unleashed" or directly with the executable "MXvsATV.exe" does absolutely nothing, also tried running as Administrator.
Reinstalled the game a couple of times but situation is unchanged.
Edit: reinstalling into a different location (with Galaxy) launched the game properly again. Also this discusson on Steam suggests that you need to replace the executable after some time:
https://steamcommunity.com/app/359220/discussions/0/3130541756151469955/