Bad video quality - any guess why? (1 Viewer)

[matis1]

since some weeks i have a seriously bad picture quality. the colours seem to have steps as they change like if i had a 16-bit picture.
i tried different codecs, i tried a dvd with power dvd, i installed powerstrip - no improvement.
does anyone have a clue what i could do else?
to have a better understandiing i attached two screenshots