Hi,
Be sure that you are using a performance program that will acutally stress test eight cores.
Try the below two patches from Microsoft for the AMD FX-8150 processor.
Another place to look is at the system configuration. Open up the RUN windows and enter: MSCONFIG
Now click on the Boot tab then Advance. Be sure that the number of processors and memory is unchecked. See the below image.
If the above suggestions don't fix the issue then trying clearing the CMOS.
Happy Thanksgiving!