Samsung LED TV problems?

I bought a 40 Inch LED 7020 TV. The problem is the picture setting is not stable. If I use (for instance) standard mode then after a while it changes automatically to the dynamic mode. I want to see mild pictures and the dynamic mode delivers very sharp and bright pictures.
Anyway, I don't know what kind of problem it is? I am not sure whether it is software problem or hardware problem? I wanna get rid from this problem and I will appreticate if someone suggests something. Thanks, Shanto.