My sturdy and largely trouble-free Garmin 800 has suddenly gone blooey. When I plug it into my iMac, it doesn't go into data storage mode--that is, no icons
appear for Garmin and the SD card on the desktop. Instead, it begins to start up, acquire satellites, and get ready for a new ride.

After consulting the online owner's manual I discovered that if I hold down the reset button while the unit is turning on, the icons appear and synching can proceed. This works most of the time. But surely there must be a way to get it back to full, normal function?

All advice and suggestions welcome, and appreciated.