Greetings.
Since the DIMM LED is lit up, I would removing all but the minimum required DIMMs (usually one per processor).
Please keep track of which DIMM was in which slot originally.
I would start by removing all but DIMM in slot A1, and E1.
If the system is still in same situation, then swap DIMMs A1 and E1 with other DIMMs.
If this does not have positive impact, then please check/reseat all riser cards, and make sure CPUs are seated firmly.
If no progress, please remove any PCI-E cards including raid controller (if present)
Did you ever configure the CIMC? It would be very helpful as it would show the SEL logs, and possibly more details of the failure.
Kirk...