Just asking what you've done so far.
If the mini-box is plugged in, you've verified your connections are properly connected and secure and your input source is "HDMI", you could have a faulty HDMI cable.
Some other users who check these forums in the mornings may have an idea. In the meantime, you can email cox.help@cox.com and include a link to this forum thread. Give them as much specific information as you have. It will help them help you.
When you do get your TV working, please post back here what you did to fix it.