making sure the appliance is NOT plugged in.
open up the appliance with the appropiate screwdriver and with a voltmeter set to resistance, check resistors R8 and R11
they should give a reading of 50 ohms, if you cant see resistor R11 next to R8, then R8 should be 100 Ohms.
if any of these checks do not show this value or very close to this value, then it is that resistor that is faulty.
you can buy them on eBay for around £1.50.
just search for "50 ohm GHD"
to replace the resistor you will need to be able to use a soldering iron competently, if not find someone who can do it for you.
repair time takes around 20 -30 mins.
this is not the only probable cause of appliance failure , but it is the commonest one.
others are thermistor failure, heater element failure.
hope that helps
Rainman
January 2011