You are only licensed to use Rank Builder on one computer at a time.
If you want to change computers, (for example to go from your desk top computer to your laptop), you have two options. The first is to buy two licenses of Rank Builder. The second is to "reset" your license.
To do that, go here:
http://www.linkbuilder-pro.com/reset_license.php
When asked for "Email" and "Password", make sure you enter the same information you used to "activate" the software the first time.