I recently upgraded my CPU and came across this problem.
Whenever I reboot or shut down my pc and boot it up it hangs on BIOS boot screen (the one where it says bios version etc.) and is just stuck there. Only workaround for this was to shut down pc and wait about 10 minutes and then boot it up.
On another note, CPU I got had voltages weird, AMD Phenom II X4 965 Black Edition and CPU-Z showed vcore 1.568, I panicked and fast changed it to 1.4 (stands at 1.38 now) in BIOS.
Is there any way to fix this issue? BIOS is on most recent patch/update according to Gigabyte official site.