I fixed this on my system by updating my video drivers.
I had this same problem, where content just stopped playing all of a sudden without any changes on my system shortly after updating iTunes to version 12. I tried all of the various fixes suggested on this post, but none of them worked for me.
I also found that if I waited a very long time after the screen went black, the video would eventually play, but without audio. I confirmed that audio was working by testing the output through the control panel.
What eventually fixed it was updating video drivers from the ASUS supplied driver to the Intel HD4000 latest version direct from Intel. It works perfectly now.
FWIW, my setup:
ASUS Mainboard Model P8H77-M
CPU: Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz
Windows Version: Microsoft Windows 7 (6.1) Enterprise Edition 64-bit Service Pack 1 (Build 7601)
DirectX Version: 11.0
Old Driver Version = 9.17.10.2867
New Driver Version: 10.18.10.4061
Shader Version: 5.0
OpenGL* Version: 4.0
OpenCL* Version: 1.2
Physical Memory: 7881 MB
Processor Graphics in Use: Intel(R) HD Graphics 4000
Video BIOS: 2124.0
Current Resolution: 1920 x 1080