Update, 3/10: WinAtlanta is back up; domain registration was renewed for one year. BigWinCity.com has not yet been renewed yet (or at least it’s not showing up yet as such).
It appears that the owner(s) of WinAtlanta (and the other sites aliased to it, including BigWinCity) has decided to let his domains go without renewing them. WinAtlanta.com expired on the 2nd and is now a “pending renewal or deletion” holding page from registrar GoDaddy. BigWinCity.com expired yesterday but is still coming up, so you can access your account from there, though I don’t know for what purpose. If the site owner isn’t renewing registration, there’s no reason to believe he’s going to honor any prizes.
I contacted the owner at the registration information on file with GoDaddy and asked for a comment. Will update this if I hear back… otherwise, I think we can assume the site is kaput.