Other Reasons Your system may be slow
Dirt and Dust
Look at the back of your computer, how much dust is there? If it looks like the lint tray from your dryer, this may be slowing your system down. CPU's (Central Processing Units) generate a lot of heat. The problem is that they need to stay cool to operate. The solution is that CPU's have heat sinks and fans which keeps them cool. That fan you hear in the back is sucking air in to keep your CPU cool. If you see a layer of dust, then your CPU is not getting enough cool air to keep them running at optimal speed. When modern CPU's do not get enough cooling, they are designed to slow down and in many cases may shut down. Simply clean the dust and you may notice a considerable improvement.
Imminent Hard Drive Failure
All Hard Drives fail eventually. You can expect about 5 years from a hard drive. Some will last longer and some will die quicker. If you see that you are getting write errors on a frequent basis or the hard drive is constantly blinking, it may be a sign that it is dying. One bad sign is if you are hearing loud crunching from your hard drive. Hard drives make noise, but if you notice the noise and it is continuous and crunching, you are in trouble.
Memory
Sometimes a memory stick in your system may die or revert back to a slower speed. You may see this after a power outtage, or if you shut your system down while it is in POST (booting). Typically if a memory module goes bad, you will hear a beep code when you start the computer. Sometimes it will still boot and only recognize the good module