1. If you use one of those all-in-one (TV / DVD / Hometheatre) remote controls, make sure to push the TV select button to operate the TV.
2. The Remote control signal range is around 6m. If the remote control is too far away from the TV, or at a 45 degree angle, or there is an obstacle, then it may be not work.
3. Take the batteries out and clean the terminals contacts with a damp towel and baking soda.
4. Change the batteries.