Nokia 6600 Won't Start and Work Properly

It all started when I switched my other sim card with the other one. I know both of them works. But now, my phone has a problem. It won't start...

Sometimes, It starts and reaches to the Main menu. After a few seconds, It automatically reboots and goes back to the Main Menu again and after a few seconds, reboots again.

Sometimes, it doesn't reach the main menu. It automatically reboots after a few seconds while in the Welcome Logo "NOKIA" is being shown...


PLEASE HELP ME ... :(

see symbian faqs for a faq of phone not starting.