I have a second-hand Xbox 360 with a huge amount of old accounts. How do I remove them? I do not have Xbox Live.
You can just delete them from the drive. Go to System, and then choose Settings (when at the My Xbox channel, it's the far right item IIRC), then Storage, and select Memory Unit or Hard Drive (or whatever storage device the console is using). There should be list of the types of items stored there, one of which is Profiles. Select that, then delete each one.