Hey there, @ErgonomicPickle!
In addition to what @Martell mentioned, I'd like to ask you if you had the secondary HDD unplugged from the motherboard while you installed Windows onto the SSD? From the looks of your Disk Management, it seems like that secondary drive is not recognized by the system at all. Make sure you check your BIOS and see if the drive is listed there, at least. Another thing that you should try is reseating the connections to the HDD and make sure you use a different SATA port on the mobo and also a different SATA cable. A failed connection is most probably interfering with the system and that's why you cannot see the drive in Windows. Another way to troubleshoot it would be to plug it to another working PC and see...