How much RAM do you have? What processor do you have? What graphics? What version of Windows? Have you run any performance tests? A good performance test is the SI Sandra one that you can download from http://www.download.com. Try that and see what it says. Just looking at your HD for performance is like looking at one tree in the forest - you need the complete picture. A chain is only as strong as the weakest link, you know.
If you have Vista or later, what is your Windows experience index? You can click Start and right-click Computer, then click Properties to see it.
Here are my hard drive's benchmarks:
As you can see it is completely garbage, and I have been getting very low FPS in games.
Could this be the issue?