Ok, first off if the TV is at fault the dead pixels will there for everything you watch even the TV's own menus.
If this is not the case then there is a well known "bug" in the SKY+HD when creates a very noticeable spot of colour (black) in the same place on the screen when playing back a manual recording or a planner recording that has the Blue Locked function enabled, in other words you have to enter the PIN to watch the programme.
If it's the latter then when it's playing press Pause then the Green button then Backup and you are back in playback and no black dot.
If it's the former then

the TV is probably damaged.