I'm sorry to hear that you're having this issue.
In some cases, this may be a temporary HDCP issue with the cable/sat box. Try unplugging (or refreshing/updating) the box to see if that helps. When video is not passed, but audio is, that can indicate an issue with the HDCP settings in the box. Often times, a reset can fix this.
My 3 year old samsung plasma tv has started loosing picture(but sound remains) whenever it feels like it.Sometimes turning it off for 5mins works,but sometimes not.It sometimes goes days without a problem,then it sometimes plays up every day.It does not matter what program you are watching either an hd channel or kids channel or on playback from the sky box