No drives show up in disk management but are shown in device manager
Both internal and external drives are missing from disk management, but external drives show in device manager
Please give us a little more background. Are these brand-new drives (which would need to be partitioned and formatted), or did they have data on them last week? Can you describe the circumstances around the disappearance of the data, if that is the case? What OS, kind of drives, motherboard?
By "disk management," are you referring to Control panel - Administrative Tools - Computer Management - Disk Management tab, or Windows Explorer?