You can try this:

1. Execute updater.exe. Make sure you checked "USB device" on Updater.
2. Turn off Nuvi and disconnect USB cable from PC.
3. Put finger on the left upper corner on LCD screen and hold it.
4. With other hand connect Nuvi to PC using USB cable
5. When Nuvi goes in preboot mode it will be recognized by updater. Press OK on updater.

p.s.

You can also try on step 3. put finger in the midle of the screen and hold it.