The first thing to check, if you are not able to connect the Instrument, is that the USB cable is the original one (not all USB cable work).
If you are sure the cable is original, these problems may be caused by a malfunction of the USB memory (clusters, damages …). Normally it is caused because the instrument, was not disconnected safely from the computer. In this case you have 2 ways for solving the problem: one is soft and one is more radical.
connect the Instrument by USB to a Windows or Linux computer operative system (Apple does not work for this because it hides some files) and control the files and the folders that will appear. The Compass file extensions are: “.txt” (Airspaces and colormaps) “.aud” (audio) “.car” (cartography) “.dsp” (display) “.pol” (polar) “.RTE” (Routes); “.wpt” .”geo” (Waypoints) “.task” (tasks) “.tif” (terrain). If you see different files, specially the ones that appears as uncommon or with strange names or extensions, they can corrupt the correct use of your instrument. Cancel that files and try to use the instrument again.
If the problem is not solved, it may be necessary to format the USB memory and/or the internal memory. This procedure usually definitively solves the problem but the instrument settings and files will be reported to the original manufacturing, as when you received the instrument. It is important to have a backup before formatting USB (!). To format the memory: enter in the “Configuration Menu” and scroll the menu: at the end you will find the buttons for formatting the USB or/and the internal memory. Just press and confirm.