My TV has a red x in the middle of the screen

The make and model would be helpful, but firstly try completely disconnecting it from the power and starting it up again.

If you can, take a picture of it and post so we can see what it looks like.

Also, use a flashlight on the screen when it is off. If you can still see it when the TV is off and shining a flashlight on the screen, then you probably have a cracked screen. This type of problem is beyond economical repair.