how can i restore my iphone? it doesn't work when i restore my iphone on itunes, unknown error occured (9), what will i do? apple logo always hanged.

http://support.apple.com/kb/TS3694#error9

The first troubleshooting step is to use a USB port directly on your computer, not to a USB hub. If it is a desktop or tower case computer use a USB port on the back rather than the front (front ports are usually an internal hub). Also disconnect other USB devices except mouse and keyboard.

The next step is to disable your antivirus and firewall, which may be blocking the USB connection.

If the problem is not resolved try restoring on a different computer.

All of this assumes the phone is not hacked or jailbroken; if it is, then that is the cause of the problem.

Try this article to troubleshoot your error.

http://support.apple.com/kb/TS3694#error9