8GB Memory Card Does Not Work

My Canon 650D camera has an 8 GB Sandisk Ultra memory card. When I try to insert the card into my Mac, nothing shows up, be it in my finder or in the devices. I inserted my card into a friend’s Mac and it worked just fine on hers. What seems to be the problem with my device? The only noticeable difference between the two Macs is that mine is a 15-inch and hers is a 13-inch.

Thank you!