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With these symptoms, it sounds like the board is not even passing BIOS POST. The Service Processor is an embedded, independant system, which is how you can still connect to it - in other respects, troubleshooting is as with similar x86 boards - I see you have tried moving the DIMMs around (although from memory there are two sizes in a FAS3210 - 2 x 2GB + 1 x 1GB) - have you tried to swap all the RAM between both controllers? and disconnect and reconnect the NVRAM battery? If the other controller doesn't work with the same DIMMs, then that is obviously the cause.. As a last ditch, I would attempt to source another Intel E5220 processor and swap it in - they are only a few dollars on eBay. I would also check the surface mount capacitors (especially C10) near the rear corner of the board - they can be easily damaged and it will prevent booting.
I've found some other cases, and unfortunately the problem is probably with the motherboard, and it is not something repairable. Assuming you are still running ONTAP 8.0 or 8.1 - the licenses are not node-locked, and a replacement motherboard from the used market would be your best option.