If it has been working, why not try a factory reset, can't do any harm, there is a reset button behind the AV socket on the back, press it with a pin.
I had one that arrived to me like that, and I had to send it back, there was nothing That could be done - tried everything the chinese guys told me to do to no avail.
[video=youtube;EAJtEXJbvd4]https://www.youtube.com/watch?v=EAJtEXJbvd4[/video]