It may be your lens have dust, but you didn't pay attention, you can put it in it. Or look for professional help.
Yes, in my opinion you should change lenses of your camera and then give it a try again. And still you get some problem then definitely choose professional help.
Thanks everyone for your thoughts... my camera is now at a Panasonic authorized service center. They say they have never seen such defect, but they didn't give me any more information about it. Better let they handle it, the way it's going I think they'll get me a new camera ....