Nokia n79 keypad problem

Nokia N 79 keypad problem, the cellphone work normally just for a minute, after that the cellphone will stuck/hang, all the keypad not function, except switch on button.

for this problem :

1. Check/replace if needed volume keypad/volume button
2. If the problem not solved try to check other keypad, maybe short each other.
3. If the problem not solved, try to flash/upgrade software/firmware with a newest version.
5. If the problem still not solved check Keypad IC /Upp/cpu, resolder or replace if needed.