According to the A780GM-A Ultra motherboard manual ...http://eudownload.ecs.com.tw/dlfileecs/A780GM-A%20Ultra%20v1.0%20-low.pdf
... its chipset incorporates an AMD 780G NorthBridge and an AMD SB750 SouthBridge.
The A780GM-A (V1.0) uses a different southbridge, namely the AMD SB700:http://utrade.cl/catalog/down/A780GM-A(V1.0).pdf
I suggest you look in Device Manager to determine which chipset you have, and then update its drivers.
I don't know whether the following URL is safe, but it looks promising:http://drivers.downseeker.com/download/4619/amd-690g-780g-790gx-sb400-sb450-sb600-sb700-sb750-driver-10.2/
Some early chipsets, eg NVIDIA NForce, had a 1TiB limitation in their drivers, but a driver update resolved the issue in those cases.