Safely Remove a USB Drive
From ATTWiki
Some USB drive users remove the drives from Windows USB ports - only to discover later that the files or the drive has become corrupted.
In most cases it is best to right click on the icon in the notification area (or system tray) that shows a small left green arrow. Wait for the bubble to pop-up showing choices to devices to disable. Choose the appropriate device with the mouse. Then wait for another bubble to pop-up that reports it is safe to remove the drive.