Chosen Solution
I have an iMac 5K 2019 where I’ve replaced the stock RAM with two plates 8GB (2666MHz) each (HyperX HX426S15IB2K2/16). Today I bought two more identical modules and tried to install them. So now I have 4 identical modules. But my iMac didn’t start. I can only feel that warm air is coming from the iMac, but nothing more: the screen is black. I’ve tried next configurations: It boots with any single module installed in any slot;It boots with any two modules installed in slots 1+3 or 2+4;But it doesn’t boot with any two modules installed in 1+2 or 3+4 slots;It also doesn’t boot with any thee modules installed in any thee slots So I think, that modules are ok, and the slots are also ok. So what could be the problem?
Give this a shot. Install all the RAM. Now we are going to zap the PRAM. Hit the power button and immediately hold down the par,option and command keys and hold them down. The machine should reboot. Continue holding down until it tones three times and release the keys and allow it to boot. UPDATE 4/19/20 RAM Type:PC4-21300 DDR4Min. RAM Speed:2666 MHz Details:Supports 2666 MHz PC4-21300 DDR4 SDRAM SO-DIMMs (260-pin). Standard RAM:8 GBMaximum RAM:128 GB* Details:*By default, 8 GB of RAM is installed as two 4 GB memory modules (and two slots are unoccupied). For some curious reason, Apple only permits this model to be configured at the time of purchase with 16 GB or 32 GB of RAM for an extra US$200 or US$600, respectively. However, as first determined by OWC, it actually can support up to 128 GB of RAM with four 32 GB memory modules. At this point I would replace the original RAM and then attempt adding your new RAM. Also your new RAM may just not be compatible with this MAC. I would also contact Kingston and ask if the HyperX HX426S15IB2K2 is rated for this iMac.
It does take a bit of time to boot when the system needs to validate the new RAM config. Put the RAM back in make sure the RAM is fully seated. Restart the system, let it sit for a half hour the system should have booted by then. If not take the original RAM out and put the new RAM in its place (slot for slot) did the system start up then?
I had the similar experience today. I bought upgrades for two 16 gb rams, definitely different brand from what’s original to my iMac, and it wouldn’t start. So what I had installed were 4 gb original rams on slots 1 and 3, and added the 16s to slots 2 and 4, and pc would not boot. I could hear the machine work but nothing loads on the screen. I heard this could happen if your rams are not identical. What I did after is I took off all rams and added the 16s I got to slots 1 and 3, and viola! It worked perfectly. I think it’s probably the ram channels wanting the same ram profile. As for your case, I am sorry it’s not working with all 4 identical rams. Maybe try using just slots 1 and 3 with identical rams? Also make sure they are placed correctly and push them all the way in.
