strange block of windows during playback

[zameis]

when I play back an .mpeg 1 or 2 file with any player on my pc there are strange white blocks, 9 of them like a window pane floating around the screen. It only happens on 1 pc not on my other pc with the same file.
also, if I encode on that pc the blocks show up on the conversion mpeg2 when I burn to dvd and playback on my dvd player.

any idea as to what this is, it only started showing up several days ago.

[zameis]

please help