[jpstewart]

First off, you should see a minimum of three LEDs lit on the frontplane:  the BaseIO and Heart LEDs should be always on, plus one for the graphics card.  (And more if you have the PCI cage or other XIO cards installed.)  You need to figure out which LEDs are lit and what's missing:
https://wiki.preterhuman.net/SGI_Octane#...plane_LEDs
http://www.sgistuff.net/hardware/systems...l#problems

Secondly, there's no jumper to stop the automatic power on.  That's a symptom of a bigger problem.  A normal Octane won't do that.  I seem to recall mine did that once after swapping some components.  But only the first time I plugged it in.  After a normal boot-up and power-down cycle it returned to normal.  If the behaviour persists on yours, you'll need to track down the problem.

Oh, and finally, that's not a serial port on the frontplane of the Octane.  It's an undocumented header and the connector is always omitted.