Kingster1 - First thing I'd recommend you do is send an email to firstname.lastname@example.org and explain exactly what you've done along with the problem. If its just some weird registration issue, they can sort you out on their end.
I'm assuming you have the steam version of the game. I'm just going to throw out some things that might work for you. Some folks reported having issues logging in through steam directly (eg launching Demigod from steam). For some, simply running steam as an administrator seems to help. Try that if you have not already. For others with the same problem, they were able to get things working by running Demigod OUTSIDE of steam as an administrator. There's a file called Demigod.exe. Its somewhere in the steam directory - I don't know the exact location off the top of my head, but you should be able to find it by doing a search for demigod.exe. When you find the file, adjust the properties to run as administrator. Then run the game and try to log in to multiplayer. If either of those work, please reply here.
You can double check and confirm that you successfully registered Demigod to your stardock account by going here and seeing if it shows up registered to your name (use your stardock username and pw): https://store.stardock.com/login.aspx?ReturnUrl=/myaccount/products
If it doesn't show up, then register the game to your SD account using this link: https://services.stardock.net/accounts/registerproduct.aspx
Anyway, provide feedback and as many details as possible. Hope this helps you and sorry its been a pain to get playing.