4 Core CPU,but only 3 cores usable

[screappy]

So I am having the AMD Athlon x4 760k Quad Core Processor,but I can't use all cores.I was able to use them before but not sure what happened,I can use only 3 now.

http://i.imgur.com/ut2cRcf.png
http://i.imgur.com/l8Fa1s3.png

 

[Karsten75]

There is something called "parking" - some people do it, not sure why?

http://lmgtfy.com/?q=amd+parking+processor+core

 

[screappy]

I believe this is something different,like tweaking the CPU,some sort of overclocking.