Leonardo as Unknown USB device

Hello comrades! One day i connect my Leonardo to PC(Windows 8.1 x64) and found what my leonardo board not recognizaed by Windows. In device Manager it appears as Unknown USB device(Device Descriptor Request Failed). Power led is On, L flashes after plugging or reseting, after L flasehes RX led is on. List of things what i'm already try: 1. Reconnect Arduino. 2. Restart PC. 3. Reinstall FTDI drivers. Can anyone help me? Best regards, Daspisch.

The problem was in broken firmware. After reuploading bootloader to my Arduino using USBasp all works greate.