webcam

My question is I purchased a webcam , I am using it with a family member that has one also. Mine is a phillips a cost of 50.00.... Everything is fine on using it, until I put it on FULLSCREEN to see them. Then there is a full clearpicture, BUT SHAKYBOX look in the front of the fullscreenpicture movement.......... They say other family members do not say any thing when they have there,s set on fullscreen.  I don,t no what to do. I am fine leaving it on a smallversion,   seeing them...........BUT as soon as I go fullscreen  the small checks our there with a movement????????Thank yoy    JanetH