alexoiu :
Then the board does support the 8320.
you 100% sure? a few of places seem to sell them together as a bundle:
http://www.amazon.co.uk/AMD-FX-8320-Vishera-Core-3-50GHz/dp/B00A0K628E
https://www.csl-computer.com/shop/product_info.php?products_id=5946
The ASUS website also says the are compatible (i think?)
http://support.asus.com/cpusupport/detail.aspx?SLanguage=en&p=1&m=M5A78L-M/USB3&cpu=FX-8320(FD8320FRW8KHK,3.5GHz,8C,125W,rev.C0,AM3+)&pcb=ALL&sincebios=1401&memo=
and since i am on bios 1503 surely it should work? but then again i have no idea what im talking about