Elsa,
The internal microphone is going to record noises you probably don't hear while shooting. It will record almost and faint sound made by the camera. You have to get a microphone that is isolate in it's mount from the camera. You'll want a wind sock. Research and buy a mic that works with your dSLR that costs about $150.00 to $200.00 (USD). That's pretty much square one. There is nothing wrong with your camera.
Dave