I am sorry, but they are largely unrepairable.
My daughters have 2, trust me on this.
However if you ask the company (Google them) and send the product back, they will give you a voucher to buy a new set at a considerable discount.
Usual problem, cable entry point and switch become damaged. they can spark and even melt the product.
DON'T leave plugged into the mains, fires have been known and shocks, which is how i got involved.
if this is so -complain to GHD with the serial number, if its an affected bad batch, free replacement -but don't get your hopes up. ours were, still refused to replace it.
Chris
November 2007