If you cannot get sound through the TV with either the cable box or bluray then the cable box cannot be at fault. HDMI connections can be very frustrating. Try turning the source on first and then the TV.
Try different brand of HDMI cable. Try a different input on the TV.
(continuation of above)...the cable box, sound came back on but when system was shutdown it was off again. Checked all cable and TV settings and they were OK. Reset the the TV per Samsung procedure and still no sound. Unplugged the cable box and tried Netflix through the WiFi Blue Ray player & picture but no sound. So do you think it's the TV or the cable box??