Firmware update impossible

Hi!
I just bought a U-Mix Control Pro device, but the device is not recognozed (device unplugged). So I tried to follow the various issues related to this problem on this forum, beginning by updating the device firmware.
But when I press the SHIFT and BROWSE A buttons together and put the power on (on the front, the rear power button being already on USB), the source A and source B does not light up, and nothing happens on the computer side.
Moreover, the Cross DJ software ask me for update to the full version, despite I saved the correct serial number on installation process.
Could you help me please to solve this issue and tell me what's wrong?
Regards,
Maxime
I just bought a U-Mix Control Pro device, but the device is not recognozed (device unplugged). So I tried to follow the various issues related to this problem on this forum, beginning by updating the device firmware.
But when I press the SHIFT and BROWSE A buttons together and put the power on (on the front, the rear power button being already on USB), the source A and source B does not light up, and nothing happens on the computer side.
Moreover, the Cross DJ software ask me for update to the full version, despite I saved the correct serial number on installation process.
Could you help me please to solve this issue and tell me what's wrong?
Regards,
Maxime