iPhone 3GS cannot be restored to factory settings after iOS 7 launched

Lately my iPhone 3GS have some fireware issues.

Everytime i turn it on, it instructed me to connect it to itunes but it keep restarting before it can be detected by itunes within 1 min. Hence, i decided to restore it back to factory settings. Apparently failed on each attemps during Restoring iPhone firmware . Pop up window with "The iPhone "iPhone" could not be restored. An unknown error occurred (1)." appeared.

Is this because of incompatible of iPhone 3GS Hardware with iOS 7?

Your help would be greatly appreciated.

Thanks and regards,

Choon Loong