Although you can manipulate files, maps, routes and waypoints directly on your Garmin GPS device, it's usually much more efficient to connect it to your computer and use Garmin's BaseCamp software instead. Occasionally, you might find that the computer fails to recognize your device. When that happens, there are a few different solutions.
The Quick Fixes
If your computer doesn't read the Garmin, start by unplugging your GPS and powering it down. Then turn it back on again, and plug your USB cable into the device. Finally, plug the USB cable back into your computer. Your Garmin should show a picture of the GPS attached to a tower. You should also be able to see it on your computer. On a Windows 8 machine, swipe in from the right and use the search function to find "This Computer." When you run the program, your GPS will be displayed as an external device. On a Mac, it should show on your desktop as an icon labeled "GARMIN."
A Few Things to Try
If your computer still doesn't find the Garmin after you reboot it, there are a few other things to try. First, plug it directly to the computer rather than going through a USB hub or the Garmin's own cradle if it has one. You might also try it in a different USB port. Theoretically any port should work, but occasionally that's not the case. The same holds true for the USB cable. Some cables are wired primarily for charging, others for data transfer, and some for both. Garmin recommends using only its own cables, but if you have a number of USB cables on hand you can usually swap them until you find one that works.