Kenwood DNX 9280 BT sat nav unit... rebooting

[cradock]

Hello, bit of a long shot perhaps, but I wonder if there are any electronics whizzes who would know how to correct a Kenwood DNX 9280 BT multimedia unit in my car... I think it was a retrofit rather than original kit, but its stuck in a loop where it brings up the initial welcome screen for a few seconds, then turns itself off again, never getting to the main menu; this continues constantly and i can neither switch the unit off, nor get the reset button to work. I've gone through the manual and there's nothing in there to suggest what to do. I'll confess I'm an utter novice at this stuff - but are there any simple tricks to nudge the unit to work properly again? it came on spontaneously a couple of days back. Thanks in advance!