Black bars are a result of aspect ratio issues and generally need to be there in some cases. The only way we can determine if there is an issue, is if you provide more information:
What is the resolution of the video?
What is the resolution of the TV?
What device is connected to TV and is it configured to do letterbox? (the TV and/or the device connected to it may have some setting that you can use to change this)
When you play the video on the PC, does it have black bars or not? (some videos are encoded with the black bars and in this case nothing you can do)