Once you have been banned from a forum. Simply change your IP and register back again...You just have to disable all firewall from the PC and from the Router and then check again if you can login if not follow this simple resolution.
1. turn off any antivirus or third party firewall that you have
2. Disconnect the router from the modem [cable modem, regular isp modem] and try a direct connection. Using an ethernet cable directly connect your computer to the modem bypassing the router.
3. or even by changing Ip you could possibly get into the site.. you can be in touch with the current Ip from IP-Details.com ..You cannot change the ip address, if you are using static ip address.If it is dynamic ip address, you can change it easily by resetting the modem or switching it off and on.you can also use Proxy server or Hide ip address software to change the ip address