This has happened to me at least twice, once when I caught the cord with my foot (see FixAC) above and the AC adapter broke and another time when I didn't notice the AC cable had slipped out. The ZipIt? was left up and running at the desktop and the battery fully discharged. Upon reattaching power and charging the battery, the ZipIt? could not boot an OS from the SD card. Both times were with an Aliosa based OS, your mileage may vary. Reformatting the card and loading the OS fresh fixed it both times.