You will need to register on
Connect and join the
Windows Home Server beta program to obtain a product key for your evaluation software. Without that product key, you can't activate, and (as you've learned) you only have 30 days to use it. Note: the 120 day evaluation period started the day you installed Windows Home Server; it doesn't stop just because your server is in an unlicensed state.
Note: when you decide to purchase the full product you will have to reinstall the operating system; there's a time bomb (different from what you're experiencing now) built in that will progressively disable your server, and that is not tied to the product key. An overview of how to do this can be found
here.
I'm not on the WHS team, I just post a lot. :)