When a computer comes fresh from the manufacturer, it is fast, efficient and a breeze to use. However, as you continue to use your machine, the computer will begin to slow and eventually the blazing fast cheetah you first brought home has been reduced to a lumbering sloth.
First and foremost, be sure to defragment your computer. As you add more and more data to your hard drive, your computer (specifically, your operating system) will have a harder time locating everything. A system defragment basically sorts and compresses all that scattered info so the OS can find it.
Delete Old Files
Sometimes computers will run slowly because the machine simply has too much information crammed into it. Deleting old image files or uninstalling old programs you no longer use will go a long way towards speeding up your machine.
Run an Antivirus
Viruses, especially Trojans, can zap away a computer's processing speed. Running an antivirus program to find and remove these infections will improve speeds.
Your Windows Registry keeps track of just about everything you've ever done on your machine. Wiping this clean from time to time will allow certain programs to run faster and take up less CPU.
Clean the Hardware
Believe it or not, dusty cooling fans and motherboards can decrease computer performance due to overheating. Clean the inside of your machine every couple of months to ensure that it continues to run smoothly for years to come.