Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
I haven't heard back from you yet - please reply and let me know if you still need assistance with this.
Thanks for replying back to me.
Is the MacBook connected to a power supply when you try to connect the camera?
Have you tried using different USB ports on the MacBook?
Is the camera turned on?
Have you tried using a different USB cord?
Ok, when you say "The USB cord works perfectly with Photo, the recent Apple programme that updates iPhoto" do you mean it updated iPhoto with photos from your Powershot G15 camera?
Yes you could try removing and reinstalling the latest version of the application again from the Canon website.