What's wrong with my pictures?

My most recent photos taken with my digital camera are all scrambled and pixelated.
When reviewing them on the camera after I took them, nothing was out of the ordinary. When I uploaded to my computer later that night, they look like this
I stuck it back in the camera and now it says that there are no photos recorded. Say what?!?!
I’m using a Nikon digital camera and a Lexar 1G memory card.