First of all I assume you meant a Precision 5820 as the 5280 does not exist. Now it also depends on the CPU as this line from the specs indicates: ● DDR4 ECC RDIMMs - Supported with Xeon W Series CPUs● DDR4 Non-ECC UDIMMs supported with Core X Series CPU   So it depends on whether you are trying to use ECC or Non-ECC RAM specific to your CPU. Of course it is also possible that 8x8GB RAM modules are not supported.
I am attempting to upgrade the RAM in a Dell Precision 5280 Desktop computer. The user currently has 1 - 32gb ddr4 stick of ram. They need it to have 64gb in total. I don't have another 32gb stick so I'm trying to install 8 - 8gb ddr4 sticks. Now matter the configuration or number of sticks that I have installed I get a pre-boot error LED code of 2 Amber and 5 white lights which shows invalid memory installed on the Dell website. I double checked the sticks I have. They are Samsung 1Rx8 PC4 2666 sticks which according to the parts site is correct, apart from the brand name. Does anyone have any suggestions as to why I can't boot using the 8gb sticks, but it boots normally if I revert it back to the single 32gb stick?   Thanks in advance.
Dell Precision 5280 Desktop RAM issue.