The above response is ridiculous.
What you should do is just reactivate your software. This is normal if you have a student license or a home-use license with a 13-month expiration. As long as you are legal, you shouldn't have any problems.
ASD 2013 hotfix, which fixes the issue of the trial version expiration date is now available at:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?id=20784586&siteID=123112&linkID=12952913
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