How long ago was it you re-registered ?
It doesn't matter that your email address has changed provided you gave your new email address. Does your ISP or you have a spam filter, if so ensure it allows
register@avast.com.
If you could give it a day or so more if you can, if not complete the
avast! 4 Home Registration form again. When you do so there are three options, the last is 'I am a registered user and my registration has expired' or words to that effect, try that one.