Since it's appearing in Disk Management are you able to right-click it and give it a different drive letter? If that works, even if it doesn't appear in My Computer you can try to access it via Windows Explorer or a web browser by typing in the drive, for example E:/ and it should list a directory.
Also, you should be able to right-click it in Disk Management and click Properties -> Tools, then click the Check button to check for errors and see if that will function. Windows can then try to repair anything it finds to be broken.
Otherwise, also in Properties to into Hardware and see if the drive appears there, if it does click it then click the Properties button in the bottom-right of the window and then go to the Driver tab and see if you can update the driver.
That's all I can think of, sorry. Give those a go and hopefully we'll get somewhere
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