Teardowns I've Worked On
Answer to "Replace digitizer or lcd or both"Change the whole LCD with digitizer assembly is more easier. Here is a blog showing how to replace Z2 LCD, hope it does help. http://www.witrigs.com/blog/how-to-change-sony-xperia-z2-lcd-screen/
Answer to "mobile is not rebooting"Try to charge the device for a while, then see whether it works.