If anybody reaches this "bootloop" state (when drone connected to PC via USB disconnects and reconnects in sequence) - just leave a drone turned on for about 30-50 min with fully charged battery (of course USB should be disconnected too). Looks like after some amount of boot failures drone initiates a restore process automatically. At least this worked in my case with same symptoms, as TS did. As a sign of succesfull restore - a LED near SD card slot and reset button, will stop blinking. No need to disassemble a drone with this approach, I hope this will help anybody to save some time!