My gpsmap 66i starts up when usb is inserted then shuts down straight away.

As soon as I insert a usb cable into the charge port the unit shows the battery indicator then turns off. I have tried many different cables, tried with PC and tried with a conventional usb charger. I am at a wits end with this.  Haven't heard back from customer support as yet. Hope someone can help. The unit is only 13 months old.