The V6 box does have cooling vents on the top of it - they are not being blocked by anything are they? or do you have electrical items stacked together such as a dvd player etc? Heat issues will cause the box to switch off.
If the box is clear and air can easily flow around it then it sounds like you need a box replacement. To arrange this you need to send a text message to 07533051809 and someone will call you back to arrange this.