This is a common problem with GHD and other straightener models. Over time and with use, the wires become loose where they enter the body. Once taken apart it is easy to see where the problem lies - black soot will be evident caused by arcing. If your model has a "swivel cord" then almost certainly this mechanism will be the problem. I find it best to remove the swivel mech altogether and solder the wires directly to where the mech used to be.
I have fixed many in this way and none have ever gone wrong again.
Note, this job should not take more than about 1/2 hour, 1 at the very most.
Colin
November 2007