Hi there.
You can fix this by simply deactivating the Automatic sign in feature for "said" profile that logs in when you power on the console. To find the option to
deativate it follow these steps:
- When signed in hit the guide button on your controller.
- Scroll right, to the last page which is the settings page.
- Select "Preferences" from the list of options.
- Select "Auto Sign-in"
- Deactivate the option for xbox LIVE.
When this is complete follow these steps on the profile that you wish to sign in first when powering on the xbox 360, simply activate the option.