I opened Files (Nautilus) and the Toshiba drive is listed in Files but is not mounted. When I started the computer, the Toshiba drive did not mount and was not listed in Xfe File Manager. Shortly after, the power to my house went off. I was going to shutdown the computer and noticed the light on the Toshiba disk was still blinking so I decided to wait. After about an hour, the size of files copied had barely changed, I cancelled the process. The trouble began when I was using Xfe File Manager to copy 2 GB of picture files to the 'TOSHIBA EXT' USB disk on my Ubuntu 18.04.