If you will have repeated this problem thereby you have something wrong in Nuvi 1xxx.

I had similar situation several times. I must to find troubleshooting by exclusion by renaming and deleting files. It was voice, GPI, EULA and GPX files. Sometime the very big mlg_history.db file was reason for super long loading after a few hundreds of thousand km on odometer.
To enter the masstorage mode I do about next:

1. With the nuvi powered off, press and hold the upper left hand corner of the touchscreen with your finger
2. Continue to hold the touchscreen while pressing and releasing the power button on the device. The Garmin Logo should display
3. Continue to hold the touchscreen while connecting the device to your computer
4. After 30 seconds, the screen should flash white. At this point, release the touchscreen. A green progress bar should display on the device. After the progress bar completes (45-60 seconds), the device should go into Mass Storage mode
5. Open the nuvi drive that appears in My Computer or Computer

Original source is from:
https://support.garmin.com/support/searchSupport/case.faces?caseId=%7B01474db0-8dc8-11df-f376-000000000000%7D
But I usually released the touchscreen after a green progress bar display on the device and often I was waited a few minutes before progress bar display or complete. My friend tell me what he put a finger on center of touchscreen and this work too.