If you are running your own copy of ArcGIS – the Student Edition – the license is valid for one year. It is possible to renew your student license without re-installing ArcGIS or obtaining another install DVD. You will first need to get a new registration code. These are available by sending an email to it-help or to mdhyslop at mtu.edu
Detailed instructions for activating your license are available as a PDF: How to update an ArcGIS Student Edition license.
Please email mdhyslop with questions or comments.