Wired connection troubles?

So I'm just now getting online with my older 360. It's not a slim and it doesn't have built in wireless. I've hopped on here with my profile and bought points just fine (so I'd think my profile was ok). But when I go to the console it keeps telling me the Live ID is associated with a different gamertag. I don't see how that can be. I don't know what my gamertag would even be if it's not the profile name you use to sign in here. I know the wire I'm connecting with works fine because it downloaded and applied several Xbox updates. I also know the use rname & password work, as that's one of my hotmail accounts and it's still up and working with that same info. helppp