If your box is over heating first thing to check is the ventilation below the box, if it's over heating and making a noise you would guess that it's a faulty fan.
Is the box switching off due to the over heating, you might need to leave it turned off. You need to call Virgin on 150 from a Virgin phone, mobile or landline, or 0345 454 1111 from any other phone to report a fault, or wait here for one of the forum team to pick this up which might be 2 to 3 day's.
When phoning choose the option to report a fault, then ignore all the options offered and hopefully you should then be placed into a queue to speak to someone.