Maybe you have the OLD site addy in your browser??? IDK.. If Sabby's advice doesn't help, clear your cache, and all your site cookies (from here on site, not just in your browser Tools) and log out, maybe even turn off computer and come back on and that should fix most issues.
I'm unsure at this point in time whether there is any type of lock-out program that would prevent forum use. Are you on your own computer or on a library or other's computer?

Ok, I'm thinking too hard on this.