lmao...
Same thing happened to me with no prewarning or reason. At the time, I wasn't doing anything unethical or illegal, in other words nothing that should have gotten me banned.
I went to work and signed up for a new account, got right in and used it for awhile. I didn't post anything from any of my other sites that was previously posted. I came home and tried to sign in with the new account and nothing.
It definitely is an IP blocking issue from what I can tell. Just be careful because if you start posting things from the same sites as your other account, you might raise the red flag and get your new IP and account banned also.