needs to finish installing 0x80270300

Here are some links I found that might help:

http://forums.xbox.com/xbox_support/xbox_error_codes/f/4753/t/2073812.aspx

http://forums.xbox.com/xbox_support/xbox_error_codes/f/4753/t/2075996.aspx

https://www.halowaypoint.com/en-us/forums/6e35355aecdf4fd0acdaee3cc4156fd4/topics/halo-5-won-t-launch-anymore/cc538198-7f6d-4363-b7e6-47969ca6876a/posts

Seems like reinstalling fixes for other games.  Before you do that though I'd try clearing it's cache.

https://support.activision.com/articles/en_US/FAQ/Deleting-Old-Files-from-PlayStation-4-and-Xbox-One-Consoles

-Press and hold the power button on the front of the console until it powers down completely.
-Unplug the power cable from the back of the console so that the power brick in not connected to the console.
-Press the power button on the console three or four times. This will ensure that any remaining power in the battery is drained, clearing the cache on the console.
-Plug the power cable back into the console.
-Wait for the light on the power brick to change from white to orange.
-Turn on the console using the power button.