If you are fortunate enough to have a TV repair shop left in your area, they will have a simple device that will detect whether or not an IR remote is sending out any coded information at all.
Unfortunately, because there are no standards in the coding schemes used, that tester cannot tell you if a specific remote will work with your set; the term 'universal' smells like a reason for a law suit, they should be called 'multi-brand' since I also have several, including 'learning' remotes that refuse to learn from Ilo or Olevia remotes.
The testers once cost ~ $30 US but checking eBay, I found one for $10:
IR Remote tester
It could be that the receiving end in the set, the IR receiver or its associated decoding circuitry has failed.
The overall reliability of the sets (particularly flat panel) built within the past 5 years has really plummeted; there seems to be no company that is not impacted from this decline in quality.
Part of the problem lays in the components (especially capacitors) and these are all coming from China.