While a previous thread talked in length about the hdd on the formatter board failing (gulp) I found a post elsewhere that pointed the finger at the little CR2032 battery on the formatter board. . but continue to hold the reset button for about 4 or 5 seconds, then release.
fsck devsdb1 Alternatively if the image is stored on a microSD cardremovable storage then you can plug it into another Linux box and run fsck to repair the filesystems so it can be mounted again. . Release the power button.