I was in the process of erasing the HD on my old IMac (late 2008) prior to giving it away to a good cause. Was doing the highest level of erase as there had been some sensitive material on the system. On pass 4 of the erase there was a power failure. When I restarted the IMac the and tried to restart the erase I got an message that the disk could not be unmounted. Looking at the disk list in disk utility the disk has no name. Have tried all the tricks I know but can't find a way to make the disk mountable, so that erase can unmount it and rename it. Any ideas?