You could get something like the Niles CS12V...http://www.ebay.com/itm/Niles-CS12V-Switching-Systems-/282346359492?hash=item41bd278ac4:g:nIMAAOSwiONYNhfh
But, I would just get a good universal remote control and use it to control the screen as long as your screen has infrared control of it.
You may also have an A/V receiver which has 12v outputs.
Or, you may have a cable box which has a switched output on the back you can plug a 12v power supply into.
There are many ways to do this if you want it to be automatic.
- Theater, whole house audio, and technology consultation during the build and installation process in the Washington, DC metropolitan area.