have you tried restoring it to factory settings using iTunes?
If not: do it (make a backup first and use: http://support.apple.com/kb/HT4137 )
If you've already done it and the issue persists after restoring: your device needs a hardware repair.
Hi All, thank you for your suggestions, I have already solve this issue. The resulotion may sound funny, I browsed Youtube and there was one suggestion that to place the phone for 20 mins, and amazingly it worked! lol