To edit keyboard binding, click it and press the new key, or back space to clear it.
I'm following that, but nothing changes.
I'm using Linux Mint 17.2 Cinnamon 64 bit.
Anyone have any idea's

When you click and start typing your sequence is it seeing it? When you click does it change to alert you that it's now taking a change? Or has it just stayed there saying that the old sequence is still whatever it was. For instance the attached image, taken under Ubuntu which I'm running now, shows the normal screen to change key shortcuts. And then if I click say for "Launch Terminal" on the part where it says Ctrl-Alt-T, that part will change to say "New accelerator ..." because it's awaiting me to type a key sequence to alter what I'd like for "Launch Terminal". This isn't working in this manner for you?

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Thanks everything is working after I double clicked on the keyboard bindings.
Thank you for your reply.
SOLVED!

Cool! I was hoping it wasn't something different, I'd have been out of ideas, of which I only had the one ...