I had the same problem with an inherited SSG-5 wireless (5.4.0r1.0). I dont remember the exact status of the lights, but all the ethernet lights on sounds the same.
I found that if I plugged in a Lan or Wan connection (not sure which), then the device would boot. The boot messages via the Console appeared normal.
Once booted, I tried resetting the device via the reset button and the Console but neither worked. Resetting via the serial number method did work (username & password = SN).
After that, the device would work normally (ie, boot with nothing connected, normal lights) with the same firmware. I power cycled it lots of times with no problems and it has since worked fine.
I concluded that the config had somehow got itself into an unusual state (eg, powered off before the previous reset finished).
I thought it might be power as well and actually got a new one power supply before I discovered this solution (I guess the first power supply might have caused the problem if it was faulty).