my first carputer

Hi ..
this my first carputer I need some help I have toyota corolla 2009

I have M2-ATX ,629 lilliput screen and my old P4 computer I get motherboard , processor and ram from it..(can i use this motherboard and it save to PSU and my battery ??)

first I install ordinary pioneer head unit to amplified and to get my sound through AUX
then I put my case in trunk then connect the the two + and - wires to my battery ( where and how to connect the switch wire ?? ) because I connect The OEM switch wire to pioneer head unit..

how to get power to my screen ?? I cant use the 12V AC/DC power adapter because i install it in dash

can I make my auto switch to backup camera?? I don't have exposed wire

Since I can some what decipher your engrish so I will try and answer your question.

Install a power relay behind your screen using the IGN or ACC wire to turn it on. Run a 12V wire from your battery through the switched part of the relay. Use the output power of the relay to power your screen/head unit. Run that same power to the trunk to your "white" wire on the M2 PSU. Be sure and put a diode in reverse bias in line before the carputer so it will shutdown properly.