Forcing shutdown

Is there a way to force a shutdown of the N5200PRO (other than flipping the power switch)? My slimserver module has gone into an infinite loop (long story) and the disk is being thrashed endlessly with no end in sight.

I cannot get to the web interface - the Thecus doesn't respond. Hitting the regular power down switch caused the usual beep and 30 minutes later the damned thing is still going strong. Any ideas appreciated.

I should add that I do have the SYSUSER module installed and have alreay tried to kill all slimserver processes to regain control. They simply respawn!