External Lacie hard drive not on desktop after power failure

While I was copying files from my external Lacie hard drive to my internal iMac drive, we had a power failure. When I powered back up, the Lacie was missing from the desktop, and missing from the sidebar. When I run disk utility, it is listed, and when I verify AND repair disc, the software reports the drive is working. Yet if I try to mount it, or unmount, it returns the message : "Mount (or Unmount) failed...The disk “LaCie d2 195 GB” could not be mounted. Try running First Aid on the disk and then retry mounting."
I ran First Aid on the disk, to no avail. I get the same message. Any help??