How can I fix my GHD starighteners?

When I turn on the straighteners, the red LED light does not light up and the straighteners are not heating up. My boyfriend has changed the fuse in the plug but this hasnt made any difference. I bought them originally 4 years ago (seems a long time but they were £88!) and after 1 year I had the same loose flex problem as I've read with other questions, so I sent them to Jamella in Keighley with the guarantee etc. and they sent me a new pair promptly. I'm not sure if I can send them back again for this new problem. Anyone have any ideas how I/my boyfriend can fix them?

Many thanks