I was able to get the system hang again, this time I ran gdb from
an xterm. And it hung in the same spot.  However the disk drive
light was not on this time.  I still had to press the reset button
to bring the system back.

For what its worth this is what I do: start gdb on my program, set
a break point and a condition on it. run the program.
type next once, when I type next again the system will hang.  I am
a bit reluctant to try it a third time to see if it happens
again. :-)

Is there anything I should do to gather more info that could
help in locating the problem?

-Ram