Re: The ones from the black slots have SKhynix 4GB 1Rx8 PC3L - 12800U - 11 - 13 -a1 HMT451U6BFR8A - PB NO AA 1519 written on the back.  The ones from the white slots have Kingston 4GB 1RX8 PC3L - 12800U - 11 - 13 -A1 99995402 - 124.A00G 758012-1652 on the back. assuming both 5040 were working before you wanted to move ram, try install only one ram first, then add second, third, fourth.  for dual channel, install memory of same spec in same color slot. it is possible one of the ram was not seated correctly.  we all did this before by installing all 4 ram at once being speedy often times.
I happen to have 2 refurbished 5040 SFF, each comes with 2x4GB of memory. Since 5040 has 4 memory slots, so I am taking 2 memory sticks from one to add to the other.  The first 5040 has 2 memory sticks in the black slots, and the second 5040 has 2 sticks in the white slots. I took the 2 sticks from the black slots of the first one and add them to the black slots of the second one, the machine fails to boot.  Looks like I can only have either 2 4GB in the black slots or 2 4GB in the white slots, but not both. What could be the issue? The 4 memory sticks look almost identical to me.  The ones from the black slots have SKhynix 4GB 1Rx8 PC3L - 12800U - 11 - 13 -a1 HMT451U6BFR8A - PB NO AA 1519 written on the back.  The ones from the white slots have Kingston 4GB 1RX8 PC3L - 12800U - 11 - 13 -A1 99995402 - 124.A00G 758012-1652 on the back. Are those two brands not compatible?  It would be great to have 16GB of memory running. Any help is appreciated.     
Trouble adding 2 4GB Ram to 5040 SFF