Okay, have you removed (unmount it first) the SD Card from the device and used the computer to see if you can see the pictures? While it's in the computer, right click on the drive that it is and go to properties and see how much space is being used.
Give this a try
1. Go back to Home screen.
2. Then tap Apps.
3. Choose Gallery app.
4. Look at the upper left corner, and hit the View icon.
5. Then select Albums.
6. Press the Menu icon.
7. Touch Content to display.
8. Then untick the Cloud storage solutions like Dropbox, Facebook, Picassa, etc.