Can not bring up ispconfig

I can not bring up ispconfig in my browser. My website is running ok, but I can not get to server to modify any of the ispconfig settings. It is telling me 404 error file not found. The requested URL was not found on this server. I entered my domain followed by /81 and that is how I usually entered the servers ispconfig before. Help....!!!

 

It's :81, not /81.

 

thank you falko

Thanks for that info. I was freaking out.