Thanks for your advice. Complete newbie to DIY. Have I hit a stud or lintel or pipe?? I was installing a floating shelf - 3 screws went in easily It, but the last (closest to the corner) wouldn't drill. I was using a Redi drive self drilling plasterboard fixing and it wouldn't go further. I ended up drilling a hole and trying to put a white rawl plug in. I could get it most of the way and insert the screw. When I realised the wall wasn't hollow there by knocking (too late I couldn't get the plug out). I Invested in a stud finder that was going haywire in the room including where i drilled in the corner (metal, electricity). There are no sockets within 3 feet. Concerned I may have hit a pipe but could it have been lintel or stud ? The bathroom on the floor above sits above this room. Thanks for advice.