cores and threads

i upgraded from a Intel Pentium dual core to intel Core i5 3570 3.40hz that has 4 cores 4 threads but my pc using only 2 cores i tried every possible way to enable all cores although my BIOS shows that i have 4 cores is there any way to fix this problem ?

We all know that on paper the 5950X has four more cores and twice the threads compared to the 5900x, but when it comes to how each core was architectured, engineered and made, is there a difference there? Because if the only difference is that AMD decided to just add four more physical cores...