I'm assuming this is your Motherboardhttp://www.directron.com/blkdg31pr.html
It has a LGA 775 socket which is pretty old. If you want to play graphics intensive games such as BF4 , you might want to change your Graphics card , but the best would be to upgrade the Motherboard , CPU , GPU , PSU , and RAM.
The best upgrade for your current CPU would be thishttp://ark.intel.com/products/35428/Intel-Core2-Quad-Processor-Q9650-12M-Cache-3_00-GHz-1333-MHz-FSB
It would be difficult to find a new one , but there are many refurbished ones
Like I said , if you want the best performance , just upgrade everything.