I phoned Magellan support, got a responce right away, seems to be a good company to deal with
their solution
Thank you for contacting Magellan Technical Support. We apologize for the inconvenience that you are experiencing right now.
Please try this step on that might resolve the issue of your Explorist 400 unit:
Please press the Zoom out, Go To and Power buttons of your GPS unit at the same time.
Wait till the unit powers on and check if it will still show you a black screen.
If the unit will show you the original start-up screen, then you can go ahead and connect your GPS unit to the computer and download the firmware update.
Please be advised that it is natural for a GPS unit to be corrupted once you the downloading process of the firmware update is cut by a computer power failure.