I'm still waiting for delivery of a pre-installed SD card and card 
reader from The PiHut for my Raspberry Pi so, fed up waiting, I bought 
another card reader from Anglian Internet in Norwich.
I can now see a 16GB card from my digital camera, but the machine still 
won't see the other two 8GB cards which I used for a previous attempt at 
writing images.
Are they toast or can I recover them in order to write images to them?