If you have a dual or quad microprocessor installed, there's a good chance you're running only one of them, as that seems to be the default, in which case you're losing out on performance.
Multi-core processors range through 2, 4, and 8 cores. Each core handles two processing threads. Not all programs take advantage of multi-cores, but most games and other processing intensive programs do.
You can check whether your PC is set up correctly by typing msconfig into the Start menu's Run box. Select the Boot tab.
In the Boot tab, select the Advanced Options button.
At the top left is the Number of processors checkbox. Select this and the dropdown.
In my case, I have a 4-core processor, so I set it to the maximum. If your PC has a dual core processor then it will show only 1 and 2 in the dropdown list.
Then continually click OK until you've exited msconfig.