Hmm are you sure that the 0 ohm resistor R238 under the cpu is passing true, see drawing diisplay-connector-info. Are you sure that your front display is working. Are you sure that your simcard is good, and so does not have a internal short. And, be sure that the famous Q8 circuit is fine. More about this, see the sim-card-issues topic But also, did you have checked the serial port if it gives some information with a 0 modem serial db9 cable. Tested without and with a simcard/front panel.