4 cores, only using 2....

Solution
It is showing all 4. Notice it shows 4 logical cpus in your last image. Windows recognizes the cpus modules as the 2 cores each module can process 2 threads which equals the 4 logical processors.
You have a dual core processor with 4 threads. 1 core 2 threads. Threads are logical processors. Don't worry. If it says it uses 2 cpu then it uses 2 cpu/4 threads.
 
Because of the way the CPU is designed, it shows up as 2 cores in Task Manager. However, each core has 2 logical processors, which is why you see 4 logical processors in Task Manager and 4 cores in Device Manager.

Don't worry, all the cores on your CPU appear to be being used properly.