Try the following.

Force to Mass Storage -
Turn unit off.

Hold the lap button while plugging the unit into the USB.

Continue holding the lap button for 30 seconds and the unit should go to mass storage.

Try forcing it into mass storage by

Force to Mass Storage:

1. Power the device off
2. Press and hold the lap button while plugging into USB
3. Wait 10 to 15 seconds and device should go to mass storage

• Power the device off
  
• Press and hold the lap button while plugging into usb (with or without factory cable)
  
• Wait 10 seconds and device should go to mass storage
  

You could try forcing it into mass storage

Force to Mass Storage:

1. Power the device off
2. Press and hold the lap button while plugging into USB
3. Wait 10 to 15 seconds and device should go to mass storage

Have you tried

Force to Mass Storage -
Turn unit off. Hold the lap/reset button while plugging the unit into the USB. Continue holding the lap/reset for 30 seconds and the unit should go to mass storage.

I tried the Force to Mass Storage a couple of times before I eventually found my Garmin cable in the box. Th lap/reset did not solve the problem, but as you can see, the Garmin cable did. Thanks.

• Power the device off
  
• Press and hold the lap button while plugging in the cable USB that is attached to the computer
  
• Wait 10 seconds and device should go to mass storage
  

Will it mount to a computer?

Force to Mass Storage -
Turn unit off. Hold the lap/reset button while plugging the unit into the USB. Continue holding the lap/reset for 30 seconds and the unit should go to mass storage.