Vocore screen issue after update firmware

I BOUGHT A VOCORE 5INCH, BUT WHEN I CONNECT IT TO THE PC IT FLASHES AND THEN THE SCREEN IS BLACK, THE PC DOESN'T RECOGNIZE IT. AS IF IT DIDN'T HAVE FIRMWARE IN IT... I HAVE ANOTHER VOCORE 4INCH AND AS SOON AS I PLUG IT IN I READ THE WRITING AND THEN IT WORKS