The unit waits in pre-boot mode for ~30 seconds. If nothing is flashed to it in that time it will go the the calibration screen and then boot [if it's able].

Read carefully post #1. Make the cure firmware and load it to updater.exe and have that visible on your desktop with the radio button beside 'USB Device' selected. Hold the top LH corner of the screen while plugging the USB lead into the nuvi [have the lead ready, plugged into a rear port of your PC]. As soon as you see the nuvi's details appear in the window to the right of 'USB Device', press OK on updater.exe and keep holding the screen at least until you see 'Loader' appear on the screen.

It will go to the Logo again on boot and stay there, but you should then be able to access Mass Storage Mode. Reformat using RMPrepUSB only [see link, post #1]. Create a root folder named Garmin on the unit. Finally load the original firmware, then connect to WebUpdater to replace voice files etc and MapUpdater to replace your purchased maps, or if you have a backup restore from there.