Remotes stopping on Sylvanias is a fairly common issue, you are my second of the day...
The first thing is to confirm your remote is sending something, look at the remotes led located at the end of the remote, to the naked eye it doesn't light up but if you look at it through an SLR digital camera it should glow white when you push the button.
If this is ok then check the front plastic cover where the receiving led is on the the TV, it should be on the front of the tv. Make sure it is clean and unobscured.
If still no luck then the IR led or its interface has failed inside the TV.
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