HDD not detected while SSD is plugged in

[HallmetW]

Hey all

My problem is that when my Samsung 960 EVO M.2 SSD is plugged in, my HDD is not being detected, not even in BIOS. But if I take the SSD out, it is being detected.
I've tried swapping the M.2 slots, swapping SATA ports, referring to the manual etc.
My motherboard is a MSI Z270 Gaming M5.
I have also tried formatting the HDD with a Windows Installation USB. I've also connected that HDD to another PC with an HDD and it was being detected on there. Somehow, I believe the SSD is disabling the SATA ports but I've looked at the manual to see which ones would be disabled and even if I plugged the HDD in in the ones that aren't disabled, it still isn't being detected. I've tried everything I know but I'm running out of options.

I hope that you can help me because it is really irritating to work with such a low amount of storage.
Thank you.

 

[Paperdoc]

Your SSD fits into a mobo M2 socket, and is not of the "PCIe" type. See your mobo manual on p. 33 - special attention to the table at the bottom, the second-last and fourth-last columns. When you mount your SSD in one of the mobo M2 sockets, that DISables a specific SATA port. IF the SSD is in the M2_1 socket (with the other socket unused), then SATA Port 1 is disabled. Alternatively, if the SSD unit is in the M2_2 socket, SATA Port 5 is disabled.