The third HDD is not recognized - what could be the reason?

Question

Iron

Was:
Mother P. MSI Z77A-G43, 2xSATAIII, 4xSATAII.
Two HDDs, the main one with OS in SATAII, the second one in SATAIII.
Became:
Added an SSD, connected to the second free SATAIII (in the figure at the top left). During installation, I removed the main HDD from the wires in order to shift it to another slot. Returned the wires.
Now the OS is on the SSD (Windows 10), but the former main one is not visible through diskmgmt. Tell me, please, what is the reason? Offended? Not enough food? Maximum 2 HDDs? To put it mildly, I'm a lamer, so I don't want to poke at a poke. Thank you!
Now the slides. The top two SATA ports are white - as I understand it, SATA III.

Answer 1

It will not work without a plug at all - there are several options.
First of all, I would check that all the cables are in order and connected, sometimes this is forgotten. Then - is the disk visible in bios - if not, the problem is most likely in the hardware, try changing ports, cables.
If so, try to scan the device manager again for the presence of HD (disk drive > check for hardware changes). If this does not help, I would look for drivers on the official website of the disk manufacturer, although if it worked with the same OS before, this is hardly a problem.
Good luck!

Answer 2

And the simplest question: do you have the necessary SATA ports enabled in the BIOS?