The 360 gives 2 sets of error codes. The first is by showing one
or more red LED lights that surround the power button. The second
set requires you to press and hold the SYNC button, then press the
EJECT button on the DVD. You will see one to four of the red lights
light up, remember the number of lights and press the EJECT button
again; do this two more times so that you have a 4 digit number.
Convert the value of each digit to get your error code number as
per the info on Secondary Error Codes from the links below. This
will give you a more localized idea of where the problem is.