Can't connect to Airport after failed firmware attempt

I have an older Airport Extreme shaped like a flying saucer and was upgrading the firmware when it stopped and I had to force quit the Airport Admin Utility. Since then I cannot connect to the Airport and get the error message "The Airport Admin Utility was unable to read the configuration of the selected base station".

I did a hard reset of the Airport but it made no difference. Can anyone suggest a way I can fix this please?

Thanks