Do a Full phone formatting on your 6680! as steps below,
1. Make sure you have at least 3/4 charge of battery power left.
2. Backup your con cts list and personal files to MMC memory card.
3. Switch-off your 6680 phone.
4. Press and hold 3 keys; Green dial key, * Star key, no. 3 key on keypad and then press the power on/off to swtich on the 6600 phone.
Remember, do not let go the 3 press and hold keys until you see a formatting word screen show!
5. After a few minutes when the Full phone formatting completed, your 6680 will back to original system and factory settting.