I just registered a new account.  I was sending messages to all of my contacts (less than 30 people) informing them about my new email address (to update their address book) and then now I can't send anymore messages.  What happened? 

Truong_kevin, post your Hotmail account here so we can check if it could still be unblocked. In the meantime, refer to this solution article to know more about the error message you got:

https://windowslivehelp.com/solutions/sendlimits/archive/2009/01/28/This-account-is-currently-blocked-from-sending-messages.aspx