Remote

If your remote isn't operating the TV, you can first try a reset before going the re-coding route.

I assume that you have replaced the remote batteries with new matching batteries.  

• Press the AT&T button at the left of the top row of mode keys.
• Wait til the red light goes on and then release
• Hold the power button for 10 seconds to allow a reset and then see if you have a picture again.
• If not, press and hold the power button on the receiver for 10 seconds until the receiver lights flash
• Call AT&T U-verse at 1-800-288-2020 for Technical Support
• Even the automated switchboard can run a diagnostic.
• Note: 1-800-288-2020 press # for live operator after responding TECHNICAL SUPPORT to the prompt. 
• Hours: Monday-Saturday between 10:00am-8:00pm EST

The Tech Support people can walk you through the re-code process if you need to go that route.  But it might simply be a problem caused by hitting the wrong mode key.