cannot back up data to an external hard drive

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I found this answer on internet, Check if this helps you.

1. Windows Key+X > Device Manager > Click the topmost entry i.e. your device > Click Action in Menu > Click Scan for hardware changes
Now you should be able to see your USB drive

2, Windows Key+X > Device Manager > Expand Disk Drive > Locate the Drive > Right click on this > Uninstall > Reboot your computer
Now it should be detected

3. Whether the Drive is assigned a Drive Letter or not
Windows Key+X > Click Disk Management > If you see your Drive is listed there but there is no Drive Letter > Right Click it > Click Change Drive Letter and Paths > Add > Click Assign the following drive Letter > Click in the Drive Letter List Box > Choose an appropriate Drive Letter > OK > OK

4. Fix USB Root Hub
Windows Key+X > Click Device Manager > Expand Universal Serial Bus controllers > Right-click USB Root Hub option and click Properties > Go to Power Management tab and uncheck the Allow the computer to turn off this device to save power. Click OK. > If you have more than one USB Root Hub, repeat this step for all

5. Update / Reinstall Generic USB Hub
Windows Key+X > Click Device Manager > Expand Universal Serial Bus controllers > Right click on USB Hub > Select Update Driver Software > Browse my computer for driver software > Click on Let me pick from a list of device drivers on my computer > From the list, select Generic USB Hub > Next and follow onscreen instructions > Reboot your Computer

Regards,
J Wick