Test the speed of your CPU by using Windows Task Manager. It has a performance monitor that can report CPU speed as a live value and as a graph.
To open the Task Manager, right click on your taskbar and click Task Manager. Navigate to the Performance tab and choose CPU from the performance monitor list on the left. The Task Manager also displays how the current speed compares to the maximum capacity of your CPU. The exact speed of the CPU goes up when under load and down when mostly idle.
If your CPU speeds are consistently low, even when under load, your PC might be running at a higher temperature than it can handle. As a protective measure, the CPU automatically slows down to reduce its heat output.