WD External HD shuts down unexpectedly

After Years without any problem the HD started to shut down Minutes or hours after the Computer was awake. The green LED went dark. I thought it was the Power Adapter and tried a new one without success. I changed the USB Cable “negative” Than I cooled the unit (it was not very warm by the touch) but when it was cooled by a Fan the Shut down stopped. What would be the solution? Install a cooling Fan or ???

Hello, you might want to run a test using DLG, check the link below for the steps. 

How to test a drive for problems using Data Lifeguard Diagnostics for Windows