1. Check the TV's remote sensor. Make sure the remote sensor on the front of the TV is clear of any obstructions and debris. If the sensor is blocked, the TV may not be able to receive the signal from the remote.
2. Try resetting the TV. Unplug the TV from the power outlet, wait 30 seconds, and then plug it back in. This may clear any temporary glitches that are preventing the TV from responding to the remote.
3. Try using the TV's built-in controls. Most NEC TVs have buttons on the side or bottom of the TV that can be used to control basic functions, such as volume and channel selection. Try using these buttons to turn down the TV's mute function.
4. Connect a universal remote to the TV. If you don't have the original remote for your NEC TV, you can connect a universal remote to the TV. Follow the instructions that came with your universal remote to pair it with your TV.
5. Contact NEC customer support. If you've tried all of the above steps and the TV still won't un-mute, you may need to contact NEC customer support for assistance.