After using your computer for months or years it's gotten slow as molasses. It can be a recent development but more likely it's been a gradual process that you've barely registered until the realisation hits you one day.
A computer's inevitable performance degradation makes a lot of us wonder if the hardware manufacturers and software developers aren't conspiring to make you spend more. As it is, wear and tear happens to everything including electronics. Having moving parts in your hard disk and system fans doesn't help either.
By properly maintaining your computer though, you can extend it's useful lifespan. It helps to know what are the things likely to cause a problem in the first place.
Here's six things that can really slow down your computer:
A dying hard disk - The older a hard disk gets the more likely it is to develop bad sectors, or for its mechanical parts to fail. When bad sectors develop, anything stored on those sectors will be hard to retrieve. Your hard disk has to read the defective sector multiple times before it finally successfully reads the information stored there (if at all possible).
Do regular checks of your hard disk to ensure you catch a dying disk ASAP. It's better to be slightly inconvenienced than to lose all your precious data and suffer from a poor performing computer.
Low disk space - Nowadays hard disk capacity is abundant enough that this is rarely a problem. But if you have a computer that's more than a few years old, then likely the storage you have available isn't in the hundreds of gigabytes. Low hard disk space can cause overall system slowdowns as your operating system doesn't have the space it needs for temporary files or swap space.
DVD+/-R media (and drives) are so affordable nowadays there's just no excuse to archive infrequently used files and rid them from your hard disk. It's the simplest way to keep your hard disk uncluttered. Alternatively, upgrade to a larger hard disk. 500GB hard disks are well within a lot of people's reach right now, and you'll probably get a small performance boost in the process if you have a hard disk that's more than a couple years old.
Low or insufficient system memory - People tend to install software that they end up never using. Usually because it's free. Be mindful that more software running on your computer means more memory consumption. Things get worse when you unknowingly install a memory hog and hundreds of megabytes of memory get allocated to it for no clear reason.
Memory is cheap enough now that even the lowest end computers can easily come with 2GB. Of course, it's a better idea to uninstall unused software. This not only reduces hard disk space usage, it also reduces memory requirements if the software runs a background system service.
Unnecessary software - With internet ads the way that they are, lots of people just click and install whatever is "recommended" by the sites they visit without thinking. The result is that a lot of the software installed isn't really used and this results in software taking up memory better utilised elsewhere.
Rid yourself of all those unused browser toolbars and desktop search software. Most likely you don't use them anyway. Keep just one toolbar or desktop search software (pick your favorite vendor and remove the rest) if you really need to. Apply the same principle to all software on your computer. One software for one purpose and your memory usage will be minimised.
Malicious software - This is related to the above point. Malicious software are not only unnecessary to your system, they also pose a security risk to you personally (stealing account passwords or credit card information), and Internet users at large (botnets remotely controlled to perform illegal activities).
There are a lot of good antivirus software available for free nowadays (AVG, Avira, Avast to name a few) and commercial options are available. Keep it up-to-date and schedule weekly scans.
Windows rot - Although I've known this as a long time Windows user, it's only recently that I have learned the term used to refer to this phenomenon: Windows rot. Windows machines deteriorate in performance over time for no apparent reason. This happens even if you've maintained the system diligently. Better maintained systems merely experience this degradation more slowly.
If you haven't done a reformat of your Windows system for over a year, then you might want to look into backing up your data and going through the paces. You might be surprised just how fast your 'old' computer can be.
Often it's human sloppiness that causes performance degradation on computers. Lack of proper upkeep leads to the presence of a lot of bloat in the system and this slows everything else to a crawl. Learn to keep a neat and well maintained system, and any decent computer should easily give 5 good years of service with perhaps some relatively minor hardware upgrades along the way.