I'm not a hardware guy, but a few questions just to clarify would be: What was the last thing you were doing before it died?
When you power on does your dvd light flash once, or twice quickly?
If you have bootmii as boot2 and can't access that with a nand then it could very well be hardware. SS2 has a guide in this bricked section on restoring with boot2 and no nand backup. Check that out and hopefully if it is hardware it can be pinpointed. Good luck!