When I sold big screeen tv's a few years ago we experienced an interesting phenomena with some models...the red neon lights in the show room interfered with the infra red beam of the remote causing it to not work at certain angles so if you have changed lighting recently then this could be an issue.
to double check the remotes ...if you have a cam corder or a digital camera... the ccd sensor behind the lense can "see" the beam from the remote and will display it on the lcd display screen...using this method you can check all the buttons on the remote if you suspect one or two high use buttons have gone bad.
Finally, be careful about messing with the sensors behind the screen...I have seen repair people dislodge them from their mountings when replacing the screen causing an apparent "failure" of the sensor when in reality it just got knocked loose. Also, I hope you or anyone out there unplugs the tv before opening it and also remember that the capacitors can still hold a charge that can electricute despite the power being disconnected!
My tv does not respond to the remote control signals for power, channel nor volume. I have tried several remote controls and the all work intermittently. I have even tried changing the batteries on the remote controls. I have a 51 inch wide screen Toshiba TV. I have taken off the screen and there are 4 devises on the inside of the 4 sides of the screen. I though there was only 1 sensor. Are these sensors or is the sensor behind the screen?