So an answer for your issues even tho in not sure it’s true but it probably would help i have a precision t5500 too ,different cpu but in this case it’s not the cpu problem for the non ecc error is the bios/firmware problem and u can try update it and see if it works, and the error with the failure in the dimm slot is because the ram isn’t either properly connected and you can try switching slots and take it out and put it back in because funny story when i got the pc first time i had that issues but i changed the slot of the ram and i thought it fixed it but after a week i hit my leg in the pc and the power cable moved and pc restarted and i saw that error again and i knew what to do or either the slot or the ram is broken or the dimm slot/ram is broken and there is another thing that is the problem and it could be because you have 1 4gb ram stick and 1 8gb ram stick and i think that u cant use 8gb stick in one dimm slot.

I hope this helped even if the answer is after an year.

>"alert! memory failure detected in dimm 1"
replace
>"non ecc dimms are not supported on this system"
obviously
> it supports ecc and non-ecc memory
but not together
> Dunno many about workstations
Read the user manual *carefully* before bricking the system. Before even going to forums