1. Check the whole area and surrounding components for the keypad white LED for possible damaged, cracks, oxidation etc. Clean it first if necessary.
2. Check both of the two LED's using a multimeter. Replaced if already damaged.
3. If the LED's light are still working check the (VBAT 3.7V) battery voltage line paths.
4. Check each of the LED's positive and negative connections.
5. Check the connected resistors and coils, re-solder or replace if damaged
6. Check the LED driver transistors. Re-work or replace if necessary.
Nokia C2-03 Keypad Light LED Problem Solution