HMDI picture but no sound

i have set up a hdmi splitter box so i can watch from second box in 4no different rooms , works perfect in two rooms but in third room there is sound but no picture , i have then taken tv put direct to sky box exactly the same , then tried my other sky box threw hdmi splitter box & works , but the same fault on another tv , replaced splitter box & hdmi cable same result works then goes off ,

can any one help

regards

steve