bijers, if you did not install a fresh copy of Windows, please format your C: disk and do. Enjoy, John.
Search “CPU monitoring software”. Some software only sees your fx as 4 and not 8 cores.
I'm using an Asus motherboard as an example: You use Advanced Clock Calibration in the BIOS. Set it to auto. Active CPU Cores lets you turn cores on/off but set it to auto to use all cores.