1. use standart metod to restore firmware:
- connect computer to wl-600g and set it Ip address to 192.168.1.2/255.255.255.0
- point internet browser to http://192.168.1.1
- you must see firmware restoration page with browse button
- browse right firmware file and upgrade
2. if not firmware restoration page at http://192.168.1.1 try use under Windows ASUS Firmware Restoration Utility.