Error uploading sketches: no device found at port

Hello,

The problem is that I cannot upload sketches to my Arduino Due while it is visible both in Windows device manager (as Arduino Due programming port) and IDE (Tools -> Port). After memory erase native USB port appears in Windows as "Unknown device" instead of common "Bossa port"

I followed loop-back instructions (the pinned topic) and everything I send using serial monitor to Arduino is echoed back immediately.

IDE 1.6.8
Windows 7

If you have a clue what happened and how to fix it, please, tell me.

Thanks in advance

PS If your answer includes uploading new bootloader or smth using programmer, I have only serial one

and have no idea on how to use it with due