Paul, there should be a power indicator to show power is being supplied by the plugpack. Kinks in the low voltage side of the power supply could be the problem, overheating as the others have said and dust. Dust often has an affinity for moisture (particularly if plaster or cement are involved) and can become conductive. I'd be dismantling
the beast and cleaning any dust out. Don't try and pull it apart without a manual, they can usually be downloaded from the manufacturers site, once you have the technical manual and the associated instructions pulling apart should present no real problem.