Then we have a FAQ for "having trouble with access?"
I'd recommend following it.
Though it's long and has several steps, if each step in turn doesn't work, it has a step that tells you how to give us, the community and devs, more information to help you.
If even the final step doesn't work properly, I'd recommend total server re-install, as it likely means your server was totally exploited, and has commands embedded that prevent you from being superadmin.