I started up my 2013 Discovery LR4 and the touch screen (tactile) was completely blank, not lit up at all, just black. Obviously. this means no access to music, SatNav, Phone, etc...

 

Actually, I already found the solution to this problem: I disconnected the positive battery terminal and left it for a while. After reconnecting the systems reset themselves and the Touch Screen came back to life. The only minor problem was that I had to reset a few things, like the system date/time and a few other 'preferences'.