In this case all you can try to do is remove components like the RAM and HD to see if you can isolate where the issue is. If you can get the printer to behave differently then you should have a clue as to what has burned out on you.
If you cannot determine where in the boot process the printer is stalling then the formatter is most likely fried and the printer should be replaced.
The Service Manual does not offer any advanced troubleshooting steps for this printer model in this situation unfortunetly. Sometimes HP will lay out in detail the various steps in the power-on/boot proceedure which can be nice. All they suggest here is trying a different power source.