2001 QX4 radio help

[suckmyalpine]

im sure these questions are answered here somewhere but right now in frustrated and too lazy to look. i have installed many systems but the qx4 is giving me the hardest time. it has the navi and disc changer and all i want to do is upgrade the tape player to a new head unit. i took out both the radio and navi to put the harness for the new deck on and i didnt work at all. and now i tried putting everything back and none of it works.... can anyone help me to get it back to working and then help me install the headunit. lots of questions i know, but any help would be appreciated.