Another thing you should look at for diagnosing why your computer is running slow is the amount of memory or computer RAM you have. As technology progresses, more and more programs are requiring more ram to be able to run. Having adequate ram is essential for running these programs, especially if you plan on running multiple programs at once. RAM is fairly cheap now and can be purchased anywhere, just be sure you know exactly what kind of RAM you need because each computer is different and there are so many types of RAM.
Spyware, Adware, Malware and Other ware
The last thing you should look into for solving slow computer speeds is if you have adaware and spyware. These programs are often attached to free program downloads from the Internet and sow down your computer. They also collect information about the computer and your user and send them to a third party. These things are very dangerous and can be removed by special programs that focus on removing these.
All these things are the major culprits on slowing down your computer. If you do all of these things and keep upgrading your computers memory, your computer should be running at the speed it should.