FIFA 16 - Crashing on startup

Try going into Settings, Power, Restart Xbox.

If that doesn't help, go to Settings, Power, Turn Xbox off, then unplug the power cord from the back of the console for about 2 minutes before trying again.

I've also tried that, and it doesn't work. :/ just crashes instantly on start up. also, this was downloaded via the xbox store, not a disk version, so won't be a disk issue.

I would next uninstall the game and redownload it

I've done that. still won't open.

Are you using the account that was used to purchase the game? If so, and it still isn't working, try removing your profle (http://support.xbox.com/xbox-one/security/remove-profile-from-console). After that, do a full reboot and unplug the power cord for 2 minutes. Turn it back on, redownload your profile, and try it again.

If that still doesn't work, uninstall the game and follow the same steps.

If that also fails, I would try a factory reset of your console (http://support.xbox.com/xbox-one/system/reset-console-to-factory-defaults). If you do the factory reset, you will have to reinstall all games and apps. I would move all games but FIFA to an external hard drive first, to save you time later, if possible.