Cpuminer can only use cores it can see. If it won't use the second package it's because it can't see it.
That's an OS issue.

HWMonitor (and many other softwares) can see the second CPU, so IMHO it's not an OS issue.
If you want to further investigate the issue, I can do testing for you.
Thank you again.
You're right, it's not an OS issue, it's a user issue. The OS is only doing what the user configured it to do.