1) Go to the domain panel. 2) Select the domain (even if there is only one). 3) Click ot "Set lock" in the domain menu. 4) Fill the security question, then select "no", and unlock the domain.
It's done! very easy, this is something which you should do by yourself, it is not done by Dynadot, unless there is a technical problem.
If the domain is really BLOCKED and not locked, then there is probably a security or payment issue: you should write to support for solving that, not post on the forum.