In picture 3 you can see the backup battery compartment. You'll need a new battery, which costs about $3 (I found one at Walmart - http://goo.gl/Kjt1of). Then just replace the old battery using a screwdriver.
They're two different desks. most of the pictures were taken where I have my lights set up. The picture with the calculator working was taken on my computer desk. You can see both backgrounds in most of my other auctions as well.
For example here - http://goo.gl/yPMykF - you see the same desk as most of the pictures in this auction and here - http://goo.gl/dn57MM - you see the same desk as in the calculator working image. Notice my shadow over the card. That's because I don't have the right lights.