I have edited the title of your post to include the topic (even though there have been several replies), just "Hmmm" isn't really helpful for any future readers. Just based on your description, it would correspond with the indications of an IP block, but you can find that out by reading the "intended blockee" in the block notice. If that is the case, you can't do much else than wait or contact staff if it takes longer than a few hours. If it is specifically aimed at your account, you can only contact staff to ask for a reason.