Xbox taking long to start

Try hard resetting your Xbox, to do this you will need to press and hold the power button on your Xbox for 10 seconds then let go. After it turns off completely you can turn it back on.

Has happened to me a few times. I just shut down my console and then restart it. Usually the game in question starts up normally. If it doesn't then I would consider uninstalling game and reinstalling it.

I would unstall the game and try to download it again

1. hard reset as mentioned above should resolve the issue

2. I would always suggest restarting the console if you do not want to do a hard reset

3. Contact Us via the support page can also provide assistance, an agent can help via chat too, other options are also provided

Hope these options can help you resolve the issue, Good Luck

Try performing a hard reset EXACTLY like this. Hold the power button on the console for 8 seconds or until the power shuts down completely.
Unplug the power cord from the back of the console for 5 minutes.
Plug the power cord back in and restart the console.