C# Threading Parked CPU's?

System.Environment.ProcessorCount shows me N Processors (N in my case = 8), which I want to make use of. Now the problem is, that the windows resourcemanager sais, that 4 of my CPU's are 'parked', and the 8 Threads i start just seperate up to the 4 unblocked CPUs.

Now is there a way to use the parked CPU's, too?