Here are the specs of your PC... link below
HP Pavilion a6683w Desktop PC*-* Product Specifications*
I don't know much (anything really) about AMD or ATI but I do believe that the Sempron from AMD is like the Celeron from Intel, great workforce CPUs but not really ment for anything else, let alone gaming.
Aside from that, you have a cheesy PSU (Power Supply) and an even cheesier integrated video card so you are just lucky you can play a game.
Frankly, I don't even suggest you spending any money on a better PCIe video card since I doubt your PSU will be able to move it.
Sorry, don't mean to be so harsh or put you in a down mood, just stating the facts and the obvious. My suggestion is to save some $$$ and build your own rig next time... we will be glad to help you
Updating your drivers and doing a windows update + defaging your hdd might help a bit though