I bought a Roku Express 3900x for the kids for Christmas. It had been working without problems for the first couple of days. But since yesterday it only comes on for a short time (like 30 seconds) and then it shuts off and the white light on the device flashes twice, then stops, then flashes twice again and so on. The TV screen goes blank saying "no signal". Has anyone experienced a similar problem or does anyone have any suggestions about what could be the problem?