Q: How to restore a jailbroken iPhone 3GS?

Hello everyone,

I accidently dropped my iPhone, after that when I tried to charge the battery it ddnt accepted rather it was showing full charge signal (plug indicator). Then it got switched off. After several attempt i started showing "connect to itunes". I tried to restore by downloading the iOS 6.1, but it still it started showing error code 1602, and latest error 21. Also the serial number of phone was not showing in iTunes.

Please help how can i restore it. any possible way?