Iave a AMD FX(tm)-320 Eight-Core processor but he only run games when i put it on 2 cores in the BIOS.
how can I fix this so that I can play my games on 8 cores.
It looks like your keyboard is worn (like mine) as some numbers/letters are missing.
Assuming you mean FX-8320 eight core CPU it should work fine with all cores operating if you have a proper mobo designed for this specific CPU model, your PSU has the proper power for this CPU, you are using the correct version BIOS for this model CPU, etc. The mobo/BIOS required can be confirmed at the mobo makers website where they list "Supported CPU models" for your specific mobo model along with the required BIOS. You should also contact your mobo maker's Tech Support if the mobo and BIOS are proper for this CPU.
Depending on what version of Windows that you are using, you might also be experiencing "core parking" a know issue in Win 7-8. You might want to read and install the Windows Hot fix links below after confirming your mobo/BIOS is correct for the CPU model.