Your account will become de-activated if, for some reason, the server receives an error message when it tries to email you. See this entry in the FAQ for more.
If you can't find a way to have GTPlanet emails delivered to your current email address, then yes, you will need to use another account or create a new one.
Activation messages are sent out immediately - if you'd like it sent again, just fill out this form and it will be on its way (if it can get through your ISP's mail servers, of course!).
