That's some messed up product support. Xbox update out there that is leaving people with a black screen requiring a reset of the box. I had to log back into my accounts after that but so far looks like I fixed it.
Hope if it happens to you you'll go through this fix rather than spend an hour bouncing the thing, resetting cables, etc.
Xbox Support
support.xbox.com
Hope if it happens to you you'll go through this fix rather than spend an hour bouncing the thing, resetting cables, etc.