This worked for me on my Windows 7 system. Copied from nother

Double-click on the Safely Remove icon in your Windows System Tray. This will launch the Safely Remove program.

This icon can sometimes be hidden. If so then click on the up arrows (show hidden Icons) to the left of your icons in the tray.

The Safely Remove window will display any/all detected USB/FireWire devices connected to your Windows computer. If necessary click/check the Display device components box to expand the view.
Click on the device (e.g., external drive) you wish to remove and click on the Stop button.
A confirmation window will appear. Once again, select the device you wish to remove and click on the OK button.
A pop-up window displays notifying you that it is now safe to remove the device. You can either close the pop-up window or it will close by itself. You can now power down/disconnect your external drive from your computer.
Note: At times while Safely Removing an external drive, Windows may show a warning that the external drive is busy and cannot be disconnected. If this occurs:

Try again to Safely Remove the device or shut down your computer and then disconnect the external drive