Something may be blocking the view from the dish to the actual satellite (a tree, building works, etc)
The dish could have been "moved" (has he had anyone doing work on the house who may have knocked it out of position?)
The actual LNB (the thing that picks up the Sky signal) on the dish may have gone faulty.
The wire connecting the dish to the Sky box may have been damaged.
The wire could have become loose at the back of the Sky box.
Has he (or anyone else) moved the Sky box to do something - fit a new TV, do some DIY, put up a shelf or other job?
The wires that go in the back of the Sky box have a central core of copper and if the box is moved with the wires still plugged in it can pull the central copper core out from the Sky box.
Get him or someone else top check the Sky cables that go in the back of the sky box.
Very late in the day I agree with ickeria. If you haven't already done so, try resetting the box. (If you are not sure how to do this, pull out at the mains, wait about 20 secs, plug back in then, after about 3 minutes, you should be able to turn the box back on. This can take a little while.)