i have read what you linked to me. Honestly i don't understand a lot of it. I am using a USB to plug my kindle into my MAC, this hasn't changed as I have always done this.
I did read "In calibre, go to Preferences → Ignored Devices and check that your device is not being ignored". I'm sorry but I can't see where I find the Preferences tab in Calibre. I have used calibre for years and I just can't understand why all of a sudden it has stopped recognising my device. I have also tried my daughters Kindle and it won't recognise that either. Do you have any other suggestions that may help me download my books. Thanks in advance.