Galaxy Tab 4 8.0 frozen after rooting with Kingoroot
This state is called a soft brick easily solvable by flashing stock firmware through a flasher: Odin for Windows systems and Heimdall for MAC OS. 

You can find a complete guide + download links in this thread from XDA Developers site. There's a safe rooting process also described there. And you can learn interesting stuffs ;)

Side effects: Loss of personal data (Photos, musics, apps). 

Good luck.