Can you see the mp3's and photo's in a file manager?
Have you verified that you are indeed Internet connected by going to the browser and seeing if you can access Internet sites?
What application are you running for mp3's and photo's. Most will automatically discover your files.
Have you tried to copy them to an internal micro SDHC card to see if they are accessible? or to the internal disk of the A7?
I don't have the problem with kindle app, have you verified that uppercase/lowercase can be used vs. just lowercase in the entry of your id or password?
Are you using the standard A7 image or Dexters? Have you upgraded the OS image to the newest version?