is it possible to change the product code for DEAD phone ?...[/QUOTE]
nope
try hard-format...
1. Hold down the following three buttons: Green (call answer) button, * button, and '3' button
2.While holding these buttons, press the power button and switch on the phone
3.When the message 'Formatting' appears on the screen, format your n73...
If it doesn't work your ONLY option is... bring it to your nearest nokia care center and ask for warranty exchange / service... good luck