black screen with red X in middle of screen

If this is a wired receiver, make sure that the Ethernet/COAX cable is connected properly from the receiver to the wall/router.

Rebooted your AT&T router. Once the Broadband and Service light turn steady green, reboot the receiver.

If issue remains, perform a soft reset by unplugging the power cord of the receiver thrice (with 10 seconds interval). You will see a gear and a loading bar across the screen. 

If that didn't fix it, perform a hard reset by holding down the OK, Power, and Down arrow key simultaneously until you the three whites on the TV screen.

If issue still remains, call tech support at 800-288-2020 to have the box replaced. 

See this thread, post 20, for troubleshooting procedures with illustrations. 

Note, the last resort, described above (OK, Power, Down arrow) is called disaster recovery.  If you do that you should be aware you will lose all your recordings.  Of course by that point there's probably no getting them back anyhow!  But while you do lose your recordings you don't lose your program scheduling.  That's not kept on the dvr.

By the way, was it just an "X" on the screen or was there a number following it?

I'm happy you got it fixed. There is a way to do a disaster recovery that does NOT delete recordings...in fact, the described method might be that way.

Either way, I'm glad it didn't go that far.

For future reference, the 10-second interval thing? You're supposed do that three times.

I have a red X on a black screen with the number 3. Vodafone is of no help. Any suggestions. Wi fi is working but I cannot connect up the TV

I've got the exact same issue.....any suggestions, did you get it to work in the end?

@conall123 

In this very thread is a link to instructions on how to perform a recovery of the receiver.  There are some additional recommendations worth heeding even in 2021.   I’ll further add that putting this hardware on battery backup is worth it.