Okay, even if you say it reacts to nothing, I'm not sure if this includes the reset button, since you only talk about usb. Chances are slim, that you didn't try this, but maybe you don't know this.
At the bottom of the device, there is a small hole. In it is the reset button. You need to push and hold this button with a toothpick or something else. After some time you then have to push the power button. I hope you haven't tried this, as I don't have any idea otherwise.
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