Is his box somewhere near his cordless digital phone???
Sounds like a stupid question I know but having the box next to the main digital cordless receiver WILL affect the signal pick-up on the box.
IF he has, before you go doing something mad, try just unplugging the phone from the mains and see what happens.
If the pictures goes again then it is not that. I had this issue with the majority of my music channels, and (as I work there) I was having a conversation with someone in my team (formerly of the tech dept) he told me that one of the steps most of the tech guys miss, probably because it sounds silly, is to check if the box is next to the phone point. I tried it and it worked straight from the off, no issues since.
Another issue that it might be is a fault with the cabling. If the cable has not been installed correctly on the outside of the building (i.e. chucked over the roof or installed around a corner tightly) dampness can get in and evaporates up the wire < so you tend to find you lose the picture after it rains rather than during the down pour.
hope this might help