Chosen Solution
Hello. My Imac (27-inch, Late 2012) has the original memory (2x4GB Elpida) in slots 1 and 2. When trying to install in slots 1+3, 1+4, 2+3, 2+4 it beeps three times and the Mac does not start. Replacing the original memory in slots 1+2 with new memory (2x8GB) is successful. Can not add memory to slots 3 and 4 (old memory or new). Please advise where to look for the problem.
If you have the correct RAM, then make sure the SO-DIMM’s are properly inserted and the contacts are clean.
