I had the same problem with my LG 42PC3. I have a few remotes that were programmed to operate the television. It was highly unlikely that all 3 of the remotes were defective or with bad batteries since the other components like stereo and the cable box would work with the same remotes. I assumed the problem lied with the receiver on the TV. It turned out to be the TV but not the receiver itself. Let me explain, there is a "REMOTE IN" jack on the back of the TV to connect an external wired remote. When you plug in an external wired remote, it deactives the IR sensor. But the problem was that I didn't have an external remote plugged in there. What happens is that some corrosion builds up in the connector behind the TV which causes the circuit to close and deactives the IR receiver, all that is required is to unplug the TV from power source, squirt some WD-40 (only a little) into the connector hole behind the TV and use any 3.5mm plug like a headphone jack and plug-unplug a dozen times to loosen any build-up in the plug which I did and now the TV receives the signals from the IR remote. It worked like a charm for me....the entire fix took less than a minute. I hope this helps anyone out there with the same problem.
Thank you vp123ca! I did'nt have ear phones so I used an attachment on my vacuum cleaner and all is well:)