Open the laptop (remove the torx 5 screws holding on the back cover), disconnect the two contacts to the wireless adaptor, undo the screw which holds it in place and remove it. Then put it all back again. I added a small bit of insulation tape between the metal connectors and the securing screw for the wireless adaptor to make sure there is no electrical short between them. The fix seemed to last for a few months before it returned. I repeated the process and it was fixed again (for a while).