Do you have the orginal remote?
It can be couple of thing going wrong. If you phone has a camera in it. Turn the camera on and point the remote at it. Push the power button on the remote you will see a white light on the camera. If you don't the remote is not working.
Universal remote sometime will not work on big screen TV.
If the remote check OK. The sensor in the TV will be bad. It will need to be replaced.
you can get a sensor at www.partstore.com The cost is $2.95
You will need to remove the front cover. The sensor is either by the button on the TV or by the top of the picture tubes. You will need to unsolder and resolder the sensor in.
you can get for $2.95 at partstore.
Click here and it will take you to the part
If you have somebody do for you. It would run between $100 and $200 to get repaired.