look closely at what has been said here - it does not appear you are banned - it appears that your avi has had a problem logging out and still show in world (that is what ghosting is). Until your "ghost" leaves SL you won't be able to log back in. It isn't banned - its just a glitch.
Do you remember where you were when you logged out? What the name of the sim was? As was pointed out above - if it was a mainland sim then LL would need to be contacted to restart. (if you are not a premium member, maybe someone can help contacting live support for you). If it was a private estate then the owner of the sim or their support people would need to restart the region.
If I were logged in I would be happy to help but am not scheduled to be back there until after 3PM SL.