First thing I'd try is seeing if it's running; "service webmin status', although that may not work as not all services support the 'status' request. You could try 'start' or 'restart' and see what they report. Unless they give you some error message then I'd test to see if it works then. Otherwise have a look in /var/log/ and see if there are any Webmin logs in there (should be either in that dir, or there'll be a sub-dir).
Did you ever work this out?
First thing I'd try is seeing if it's running; "service webmin status', although that may not work as not all services support the 'status' request. You could try 'start' or 'restart' and see what they report. Unless they give you some error message then I'd test to see if it works then. Otherwise have a look in /var/log/ and see if there are any Webmin logs in there (should be either in that dir, or there'll be a sub-dir).