Just checked the manual for your MOBO here,
http://www.asrock.com/Drivers/Manual...S8X_UM_v10.pdf, and it dosent give you an option to change or set the MAC address so its not a BIOS issue.
I dont know why you have this problem, it shouldnt be that your MAC address is all zeos and im frankly amazed that you have a connection to the internet at all. I doubt drivers will fix it as you have never had to set the driver before, sooo i can only assume you have a faulty NIC.
Sorry