Seven reasons why laptops & desktops become slow 
Web Browsing
When you visit a new web site for the first time (very common occurance), your browser will do the following;
1) It records the visit in your browser history
2) The website will most likely write a few cookies to your hard drive to track your activities
3) It also saves a copy of the page (cache)
All this information is stored on your hard drive to make your next visit to this page quicker. Over the course of a few years, there will be a noticeable difference on performance if these files (records) are not cleared out regularly.
This information is of course also used by computer forensics in relevant court cases.
Temporary Files
Apart from the cache created when browsing the web, lots of temporary files are placed on your hard drive by all kinds of applications. Don't be fooled into thinking that they are as the name suggest (temporary files) as many of these files are not temporary at all.
For instance, all attachments that come with your e-mails will be stored in a temporary folder by applications like Outlook, etc. when you open them. This is sothat they can easily be opened using applications on your desktop. These files will stay there untill you delete them and are therefore anything but "temporary".
These files will clog up your hard drive and unless you reclaim this space by deleting them, your laptop / desktop will have a lot less disk space, and also appear slower.
Applications & the Registry
Everyone has applications on their machine that has only beenn downloaded for a specific purpoise and then left on the hard drive for prosperity, it has never been used since (old software from previous printers, mobile phones, cameras, etc.)
If this sounds like your machine then I would bet that your system is not running optimally (probably takes long to boot-up and memory usage is less than optimal) These unused applications should be un-installed on a regular basis, good practice, but not a complete solution.
Most uninstallers do not remove the application completely. Entries will be left in the registry as well as personal set-up files left on your hard drive to make the re-install of the application more user friendly. It is therefore very important to maintain the registry after un-installing any applications.
Be carefull when using registry cleaners though, not all of them are reputable. I can personally recommend Regcure, available @ http://www.regcure.com based on past experience and results.
The registry should be cleaned after any un-install to ensure that you do not loose any processing time on your system attempting to find uninstalled software.
This exercise can have quite a visible effect on the performance of your machine if you have performance issues due to any of the above.
MalWare
Malware is hard to detect, and can slow down your machine dramitically.
Do a full scan of your PC regularly (not less than twice a year). a Full scan could take anything from 3-6 hrs depending on the size of your hard drive and the quantity of files you have on it, but it is worth it, if not essential
Memory
With Operating Systems and Applications providing you more and more functions to make your computing experience more enjoyable, there has to be something in your system that can soak up all these instructions and present you with the WoW factor. All these instructions and displays need memory to operate in, and you could therefore easily be in need of more memory.
New technologies are being made available all the time (i.e web 2.0 - more memory per page) and these require more memory from your machine.
Always go for more memory when you upgrade your machine.
Fragmentation
Once your hard drive becomes fragmented, it can become extremely slow. The reason for this is that the file want to work with can be scattered in bits that lie all over your hard drive and these bits have to be gathered by some process to present you with the complete file.
Before defragmenting you disk, please do the following;
1. Do the clean up exercise as described above. The cleanup will create spaces on your hard drive that will help the defragmentation process.
Doing the cleanup after defragmention will not do anything for you performance wise.
2. Close all applications before doing a defragmentation (not necessary when using Vista). Files belonging to any applications that are running during defragmentation will not be defragmented.
A better practice is to defragment using windows in Safe Mode. This ensures that no background applications are running.
BIOS and Driver updates Your BIOS (see the BIOS & Password section in this knowledge base) and Drivers can also have a very big influence on the performance of your machine when they are outdated. Perform a driver scan now using DriverAgent
Outdated drivers are not necessarily compatible with new hardware, operating systems or applications on your machine and these clashes can slow you down tremendously.
Surviving the "Blue Screen of Death"
Having your machine suddenly stop working for no apparent reason is extremely frustrating. On Microsoft Windows-based computers, such failures often result in the appearance of a solid blue screen containing a cryptic message in white letters. This is commonly called the "Blue Screen of Death" or BSOD. Whenever the Windows operating system encounters an error from which it cannot recover, a BSOD is displayed.
Common hardware problems that generate a BSOD include faulty memory, a failed disk drive, or even an excess of dust on the circuit boards inside the computer. Software failures that often lead to BSODs involve improperly-installed, obsolete, defective, or otherwise faulty drivers.
A driver is the code that tells Windows about a hardware device and how to control it. Other problems could arise from improperly configured registry settings or faulty installation of Windows. Poorly written application software can also trigger the BSOD, although that is becoming increasingly rare.
It is possible for a trained computer professional to review the BSOD error message to determine what specific failure occurred, but if you are a typical computer user, you can rarely gain useful insights from this information. That doesn't mean that there is nothing you can do. Here are some simple steps that can help you track down problems and save a trip to the repair shop:
Conclusion
Look after your trusted old friend the way it has looked after you.
Keep it clean and mean.
So.. When do you Reload Your PC's Operating System?
"When is the right time to reload my PC's operating system?"
This is a question that experts have been trying to answer since Windows(r) first became popular back in the 1990s. Most personal computers start out working fine, but then, over time, their performance gets progressively worse. At some point, the computer is so dysfunctional that there's nothing left to do but just erase everything and start fresh.
Windows introduced us to the registry, a central repository that stores critical information about how your computer should be running, what software is loaded, and how it is configured. When you install or remove software, and make changes to settings and configuration options, Windows is constantly updating the registry with these changes. Over time, the registry can wind up with a lot of incorrect entries that can direct Windows to do things that it doesn't need to do.
Here are a few questions to answer when trying to decide whether it is time to reload your OS:
- Has your favourite application stopped working and even after reinstalling, it won't run correctly?
- Has your computer slowed down doing the most basic tasks?
- Are you consistently getting the dreaded "blue screen of death"?
- Has some of your hardware stopped working?
If you are experiencing any of the above, we recommend that you try a few of these fixes:
- Update all your drivers to make sure you have the latest ones installed
- Scan your computer for viruses or spyware using a commercial anti-virus program like McAfee Internet Security
- Run a registry cleaner software to automatically correct the invalid or incorrect entries
- Uninstall old programs that are no longer being used
- Check for updates to any software that cause the system to run slower
- Replace suspect hardware
If none of these fixes restore your PC back to the original performance levels you had when you first purchased it, it is probably time to start from scratch and reinstall Windows. If the PC is several years old, it may even be time to retire it and start fresh with a new computer. Run a RegistryWizard™ scan now to determine if you have any issues that can be fixed to improve your PC's performance.