I have a Garmin Nuvi 1450 LMT and have had it for a few years. Last fall I loaded a windows driver package that had USB (flashboot) drivers from Challenger Backup Solutions v 2.3.72.0. Unknown to me for a while but this caused the Garmin to not be seen in devices and printers. Also the SD card on the Garmin which usually is a separate drive letter in Exploiter disappeared.
On my laptop that had the same driver update I just rolled back the driver and all is good.
But on my Desktop with Win 7 Pro I could not do this. I did manage to manually delete the usb driver causing the problems as far as viewing the Garmin and the SD card on it.
My problem now is Garmin Express will not complete the install on the Win 7 computer. Garmin Express is how the maps are updated on the device.
Below is a screen shot of the install error. I do run the installer as an administrator.