How can I reset my car cd player JVC KD-G312?

Please can anyone help, my battery went flat on my car when I went on holiday, I cannot get my CD player on my car to switch on. I managed to download the operators manual for the JVC KD-G312, which stated to reset the CD, press the power button and the button next to the power button at the same time. I tried this and it is still not working. I know there is power going to the CD player because if I press the select button by itself the display screen lights up with some four numbers for about 4 sec.