If your HDD is detected in BIOS and shows up in Device Manager, it IS showing in Disk Management. But you may not be looking in the right place.
In Disk Management the right-hand portion has TWO panes - upper and lower - and each of them SCROLLS so you can see all they have. The Upper pane shows you all the storage devices Windows understands and can use right now. The LOWER RIGHT pane shows you those but ALSO shows you other hardware that Windows does not understand right now for some reason. That is where you should look for a "missing" drive.
Once you find it there, what does it say? For that drive there will be one large block, and on its left end will be a smaller sub-block with the disk's ID like "DISK_2", a type, a size, and a status. The main part of the block to the right will represent one or more Partitions. Each Partition also will have some information: a disk name like "BootDrive" or something, a letter name like "D:", a size in GB, a file system like "NTFS", and a status. Post here what those are.
If the "missing" unit has no letter name assigned, Windows cannot use it. In that case, RIGHT-click on the Partition and choose a letter name for it. Then back out of Disk Management and reboot to get the Registry updated.
If the "missing" unit's File System is shown as "RAW", most there is some corrupted data in the Partition Table or Directory system of the drive and Windows simply cannot understand what to do. In this case, there are data recovery tools you can get (some free, some you pay for) that will help you to recover all the files on the HDD. But to do this, you usually need a spare empty HDD because the recovery process allows you to COPY those files to a spare drive, and THEN you can repair the faulty drive once your files are safely somewhere else. (Usually a RAW drive only has corrupted data, and no actual physical flaw, so it can be repaired and re-used after you save its files somewhere.)
To deal with a RAW drive, look around the web for recovery from a RAW Format hard drive. Some software I have heard of for this includes GetDataBack for NTFS, Recuva, and EaseUS.