A low signal strength due to a bad cable could have that effect. Try another cable. It is also possible that the hard drive has failed, while the enclosure still works. Try the smartware diagnostics.
Hi there, you mention that it is “Healthy” on Disk Management, but does it show a File System (NTFS, exFAT. etc.)? If it doesn’t then the drive lost the file system. If that is the case you should be able to recover the files using TestDisk.
Also, when a drive is Healthy but lost the File System then that means that a computer error was the one who killed the FS and you should check your computer for errors or it may happen again.