Make backup of your folder GPX and then delite current.gpx inside folder GPX andalso Archive folder if you have it inside GPX.

Try this step and you will see where is problem:

remove gupdate.gcd

1.) remove img from nuvi ( add in Pc for backup)

2.) remove Text

3.) Remove voice

4.) remove keyboards

For every step you must flesh first cure to have access to mass storage and then when you create some step above flash with cure to see if your nuvi will turn on.