frragnarsson
Have you ruled out heating issues and that the cpu is throttling? Old thermal paste?
Good theory, but im partial to believe it based on 2 cores are showing, while 2 cores are not showing (within sonar) I give you props though. good reply as ive had thermal paste dry up on me before and it was a horror show to track down as I tried everything under the sun before (the last thing I checked) I checked the contact.
You are also correct in theory of thermal paste drying out because of heating issues. that stuff is hard to fry but a hot CPU, bad cooling, poor circulation will do it.
He said his Task manager shows all 4 virtual cores running so im curious if the OP made any changes to AUD.Ini or any other sonar files. I would also check AMD website for a BIOS update or even another update possibly skimping on CPU in software applications.