Problem getting into single user mode

[Margaret E. Myers]

I am hoping some kind sole on the net can help with the following
problem.

I can't seem to get the machine into single user mode. I have tried
typing "single", and "shutdown -i1 -g0", and "init 0" and "init 1". All 
that happens is that the machine shuts down and then the screen goes black
and never comes back. (I have tried waiting many (15) minutes).  I have 
to hit the reboot button on the front panel to get any response.

We have a 4D/320VGX running IRIX 3.3.

Thanx,

Margaret Myers
Naval Ocean Systems Center
San Diego, CA

myers at nosc.mil