How can I get a car stereo LCD display working?

I shorted 12v power to case, stereo works fine,just LCD display is dead. Thanks.

Simple answer?  With great difficulty.
Car stereos contain complicated microelectronics which control functions like LCD display, digital volume, amplification, front panel, tuner,etc, and these components are easily damaged by power spikes, short circuits etc. 
Higher end stereos may have better filtration and protection against these conditions but the chances are you have fried something inside and to be honest the cost of repairing it against the cost of replacing the unit, I'd say its terminal.. sorry