If not already done so, download and install the AMD Dual-Core Optimizer program which can resolve a multitude of issues with games running on these processors. The AMD Dual-Core Optimizer can be downloaded from AMD's website:

AMD Dual-Core Optimizer (It's the 2nd link down)

If already installed, it may help to uninstall it, download this one and install it again in case it is an updated version of the one currently installed.