Do a Full phone formatting on your 6600! as steps below,

1. Make sure you have at least 3/4 charge of battery power left.

2. Backup your contacts list and personal files to MMC memory card.

3. Switch-off your 6600 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 6600 will back to original system and factory settting.