When you turn on the TV there is no sound.
If you are getting no sound, but the picture is okay, first check to see if you do have sound when you switch the TV to a different source. If there is no sound from only one source, check to see that all the audio cables for that source are connected to the TV properly.
If the source is a cable box or satellite receiver, disconnect the power cord of the box for 30 seconds, then plug it back in. This will "reboot" the box.
If there is no volume regardless of what source is selected, it indicates there is a defect in the TV. The root cause involves erroneous commands being sent to the TV’s control system on the main board. The problem is most likely a faulty proximity-touch key board or push-button board, a faulty board connected in series with it, or a pinched wire going to the board, which is shorting to ground. These boards are found inside the bezel (frame) in front or along the side of the television, and are the parts of the TV that interface with the viewer, like the push-button controls, or the receiver for the remote control.
Disconnect the cable going to the proximity-touch key board or push-button board from the main board. If this stops the problem, you should replace the proximity-touch key board or push-button board. Sometimes these boards come as an assembly with a new cable. A service manual will help you specify the boards you need, and will illustrate how to disassemble the unit. Sometimes these boards are an integral part of the bezel (frame), so you may need to replace the whole bezel instead.
If the problem does not go away when you disconnect the cable, then the main board in the television may be faulty, which means you might need to replace the main board.
There are two other things that could cause the TV to do this. One of them is if there is an infrared emitting device in close proximity to the television such as a motion detector for a security system, or a neon sign. The infrared light coming from devices such as these could be erroneously picked up by the television and interpreted as a command coming from the remote control. The remedy would be to move these devices away from the television, or visa versa.
The other thing it could be is that if you have a cable TV set-top box connected to the TV using HDMI cables. It is possible that erroneous commands were sent to the TV from the cable box via the HDMI cable. This can happen when a cable service provider sends new software updates to the box. On occasion, these updates may not have all the bugs worked out of them, and may introduce incompatibility issues with the particular model television to which it is connected. The quick fix for this would be to use component video cables rather than an HDMI cable to connect the cable box to the TV. If you suspect that this is the problem, contact your cable TV service provider. They will either need to update the box with good software or replace your box with one of a different make and model.