Eventually your computer will get slowed down and even start to crash more frequently, but what causes this? This is caused by problems in your computers registry, missing dll files, fragmented operating system files. Basically everything has to break some time right? Don't worry though there are plenty of ways for you to improve your system and get it running just as fast as ever.
Defragment Your Hard Drive
There is a program called DeFraggler. This piece of software is all free and will essentially move the files on your hard drive around so they are faster to get to when your computer needs them. You can think of this like the hard drive is your refrigerator. Do you just throw stuff in there and never arrange it so you can find stuff faster? Of course not, when you want eggs in the morning you want them to be in the same spot. The problem with the computer is the same as with us, sometimes the files get deleted and then when you go and install something pieces of it get put all over the place. This makes it so it takes long for it to gather all the files and serve up the program that you wanted it to.
Defragging should be done on a weekly or monthly basis depending on what kind of use your computer gets. Don't run any programs in the background when defragging your computer either, as any files that are in use won't be moved.
Clean Up Your Registry and Old Files
Ccleaner is the program that you want for this task. What Ccleaner does is it will scan your registry for old files that are no long in use and delete them. This will speed up booting up your PC and other things because it will no longer need to search through so many registry files to look for the one it needs. On top of that it will delete your old cached files, which if left un-checked could start to take up a large portion of your hard drive and slow everything down. Make sure your internet browsers, at least, aren't running while running this software. This is because it will delete your history in the browsers as well, this increases browsing speed significantly.
Remove Viruses and Spyware
Viruses and spyware can really slow down your computer if you don't keep them under control. Not only that but they can invade your privacy and potentially do very harmful things to your computer and possibly your life! The best tool for a Windows based machine at least is Microsoft Security Essentials. It is all free forever as long as you have Windows installed.