I have a AVIC-F700BT-XS and it will light up the screen see the usb in the slot will not eject or will not accept a disc then in less then 30 seconds

all that works is the fan in the back no screen, no power to the buttons, no eject, all that seems to work is the fan it like boots no words on screen just the blue factory back ground color blue then like I said 30 seconds or less and nothing like powers down, all but the fan in the back of unit, also had a hum if I touch a rca connector to the frame of the unit firmly its stops humming. Please help which board do I need to look at replace or repair, is it the a/v board, power board meaning very bottom board, middle board I think is the a/v one and the top one not sure?? Please help me guys I need some insight to what steps or can any one tell me what the problem is could it be the main ic chip on the power board the very bottom board, I'm  kind of shooting in the dark here..