There is a file on the unit preventing it from booting. It maybe a map, a voice, text file etc. By process of elimination you can remove files/folder starting with the last ones you know were changed or added. If that's too much effort, reformat it using only [Only registered and activated users can see links. ] and then reboot it. It will create a Garmin folder, look inside to check it has also created GarminDevice.xml in there, if it's been named as a temp file then rename the extension .xml. Then connect to WebUpdater and MapUpdater to replace missing files and re-download your LM maps, or just use Garmin Express for it all. You may have to add a basemap: [Only registered and activated users can see links. ].
The loose usb port is a known problem with 14x0 units. I have a 1490 with that, simply not worth the trouble to repair it. I tape the usb/charger lead in place when i use it but eventually all those affected units' usb ports fail completely.