What you've described isn't normal behaviour for a healthy device (i.e. even a fully recovered but previously 'bricked' one) following a normal complete boot-cycle. The PC tower symbol should only be shown on screen when you connect it to a computer - although it can happen using a non-Garmin USB charging cable sometimes.

Just to be clear, please answer these questions:
1. Is there an SD card inserted in it? If so, remove it now.
2. After you loaded the original fw via 19010100780.rgn, you disconnected the nuvi from the computer before booting it up?
3. Are you sure that GarminDevice.xml isn't being created in the Garmin folder? Please check again after another boot attempt on stand-alone battery power only, if the XML is created then please post it. If instead there's a file named "GarminDevice.tmp, post that.