cannot connect to xbox live error code 8015000B

It seems that you might be facing some network, or network speed issues. Please access Settings > Network Settings > Advanced Settings > Alternate Mac Address > Clear it and the console should restart. It would definitely help if you could restart the internet router while the console is restarting.

After going through the troubleshooting steps mentioned, I invite you to perform a quick power cycle by turning off the console and then unplugging all the cables. After 2 to 3 minutes, re-plug them back again, then restart your console.

If the previous troubleshooting steps weren't helpful, a console reset would help with the system update, To reset your console you will need to follow the steps below to perform a reset on the Xbox :

Settings > System > Console Info > Reset This Xbox > Reset and Keep my Games and Apps.

Note =>The "Reset and Keep my Games and Apps" option will not cause losing your games, but please be aware that you need to be completely aware of the email address as well as the password of your account before going for it because it will require you to sign in to the account.

This problem means that you cannot connect to xbox live. Please can you use this link to help you.

support.xbox.com/.../error-code-80072EF3

Cannot connect to Xbox Live. No error code, no connection. Just says for me to do another Connection Test which works perfectly, then I go to sign in and it does it again.

The code you posted means that your console has been tampered with and cannot connect online at all as it has been banned from Live. This would be the reason it cannot take the update and there is no workaround for the ban.

support.xbox.com/.../error-code-c800-0036

the error code is saying that your internet cannot connect to xbox live, maybe due to your internet provider. It may be something you have to talk to them about.