If it says this "account" has been banned, first do not sign up for another account and play it on that computer,find a mac changer, change your mac to whatever you want, uninstalled everything combat arms, reinstall combat arms, attempt to log in back in with your account.
I had an episode earlier this year where my account was banned, and every other account I had made was banned when I logged in from this computer, I changed my MAC address and it fixed it, it couldn't be a ip ban due to the fact that we have another laptop on the same wireless network that continued to play combat arms without a problem.
I used Technitium MAC Changer v5 r3 , I do believe it is somewhere in forums here. Just do a search over the whole site.