Demigod game WILL NOT REGISTER ON STEAM

I bought this game 4 years ago and gave up on being able to play it because Stardock wouldn't fix this bug. I can't play Demigod because whenever I try to startup the game (on Steam), theres this pop-up with a "Stardock Account Registration" where I have to put in my Stardock email, password, and serial number. The Serial Number, however, will not register because apparently, it was already registered on my Stardock Account but not on Steam. This makes it to where I can't even startup the game and play it.

Please fix this.