Neo Notebook Infected with Virus

     Hu! Hu! Hu! My husband's Neo notebook laptop was infected with intense "Trojan" virus even though it has anti virus on it. We tried to clean, eliminate the threat using cleaner from the net but it cannot be killed right away. Worst is we cannot reformat it right away because it does not have cd drive. We tried to use USB stored reformatter but still to no avail. Could you suggest what to do. They said we should have a external hard drive.