How can i fix my HAI convertable straightners?

My straightners are out of warranty and i now live in the UK using my USA straightners with a converter plug. They have worked fine for over a year and now they have just stopped working! They are treated with so much care i cant live without them i dont know whats wrong with them. Can anyone help????

They are HAI Convertable Straightners 120Vac, 60hz, 40W