Computers do seem to get slower and slower, and here you will find a list of methods to help improve this, but if your computer has almost grinded to a halt then its almost certainly got a virus of some kind.
Most viruses once in a computer will usually wait until your online, then it get busy doing its own thing in the background. Your computer slows down and pages on the internet start to take forever to load.
Check your harddrive..
If you computer is more than a year old, there is likely to be some small amount of files on your computer that your computer is having trouble with. Tiny amounts of your hard-drive become hard to access due small amount of data errors, and your computer will keep retrying.. retrying as to access these files. Normally, a file loads within a fraction of a second, problem files can take several seconds to load. This all happens in the background, as your computer wont tell you this is going on until it gets to the point that it can no longer access the file what so ever.
To fix this you need to run a 'scan disk'. Open 'my computer', Right click on a drive, select properties, then select tools, then under 'error checking', click 'check now'.
Click both boxes, as to fix and recover files, then click 'start'. The computer will then want to reboot. This process can take an hour or so. Make sure you dont turn off the computer while it is doing this, as this will very likely cause permanent errors. You should really run this scan disk atleast twice a year.
Check for viruses..
Not all anti-virus software can detect all viruses, and there are a number of anti-virus software which is completely fake and wont destroy any viruses at all!
There is only one anti-virus software I recommend at the moment, and that is AVG. The best part is they have a totally free version which still kills all the viruses and is still better than most other costly anti-virus software.
First, if your current anti-virus is not updating, or you no longer subscribed to it, then remove it, this usually applies to most installations of Norton. Anti-virus software does, by its nature slow down your computer a little, as it has to constantly check that you havenít got a virus. So dont go using multiple anti-virus software, as this will often cause problems of its own.
Then search for 'free AVG' and install the free version of AVG anti-virus. This has to be one of the best free anti-virus software around.
Once installed, you should then get it to do a complete 100% scan of your system. This can take hours, so go have a few coffees, or maybe leave it running over night.
Its almost certain to have found at least one virus. Just a few clicks are required to get rid of them.
Check for malware..
Download, install 'malwarebytes'. This will find other types of viruses not normally found by most anti-virus software.
Remove unwanted files..
There are bunches of files that your computer is constantly creating which can just be deleted without any problems. These files can take up half of your computer. Most of these files can be removed very easily.
Right click on your C drive. Click properties, then just click the 'disk cleanup' button. There are more files that can be removed, but I wont cover this here as it gets a little complicated.
Your computer can often store a single file spread across 10 different locations on the hard-drive. Finding the locations and putting the file back together takes a lot longer than if the whole file was stored in one place.
Disk defrag will fix the fragmented files by putting them all back together, and thus help speed up your computer.
Right click on your C drive, click properties, then click 'Defragment Now'. Once the Disk Defragmenter window appears click the Defragment button. This process can take hours, but it depends on how fragmented your files are. You should defrag your drive atleast once a month.
Remove unwanted programs..
Its recommend your uninstall programs that you dont use, as this will help speed up your computer further. Note that deleting the icon from the screen is not uninstall the program and does not make any difference. To uninstall, either look for the ''uninstall' option in your programs list from the start button, or by opening the 'add/remove' programs using the control panel. Its recommended you dont remove programs that you dont know about, as some of these might be critical to the running of your computer.
Your should reboot your computer after every uninstall, and if you have removed several programs, then its recommend you defrag your drive once your done.
Quite a few programs will set them selves up to start doing stuff when you switch your computer on. The easiest method to stop this, is look at their options for the abiltiy to 'check for updates', and turn this function off. Real player, Media player, Quick time, Java, Google software will have software running in your machine which keeps going on-line and check for updates.
Removing internet tool bars..
I bet you have tools bars installed along the top of your internet browser! These things can really slow down your computer. If you dont use them, get rid of them! Look for the 'uninstall' option.
If you cant uninstall them, then you can remove them by looking for the 'add-on manager'. This will show what tool bars and even hidden tool bars are being used, and gives you the option of disabling them. Note that you should keep Java, Shockwave and adobe enabled, as you will find that you were using this.
Stopping unwanted services..
Services are windows background programs most of which are critical to the general running of your computer. But some services are often not used and just sat there running in your computer memory, but not actually doing anything for you.
It depends on how you use your machine to which services you could turn off. For example, if you have a PC that is wired to the internet then probably not going to be using the 'Wireless Zero Configuration' service.
Other services like 'Alerter', 'HTTP SSL', 'Messenger', 'Upload Manager' and 'Remote Access Connection Manager' can be disabled.
Disabling the wrong service will cause you problems, so be sure to know what the service does before disabling it.
To access these services, right click on 'My computer', click 'Manager', then 'Services'.
More information can be found on this page about XP services.
Stopping Indexing service..
If your not running your own web server, then its often a good idea to stop or at least slightly change the 'Indexing service'. This service looks through all your files and creates an index of them which helps the computer find files more quickly. However, it can often spend hours a day scanning and re-indexing the files, and actually have a much bigger negative effect than a positive one. Index service can also be found using the computer management console.
You can either change it as to only index the most common files, or just switch it off completely.
Internet explorer toolbars..
Most internet tool bars actually benefit the people who make them a lot more than they benefit you. These do slow your computer down. So, if you dont use them, remove them. First check in your add/remove problems. If you cant find it there, then you can disable it using the 'manage add-ons' found on your browser menu.
Get better windows drivers..
Drivers is the bits of software which helps your computer interact with the hardware. Drivers control help control the graphics on your screen, sound from the sound card, and load/save data to your hard-drive. If you have an old machine, or a machine you or someone built, then its likely you are using the drivers from Microsoft. But Microsoft didnt make the hardware. The people who did also made software drivers for them. Because manufacture knows there hardware better, then the drivers are almost always better performance. Better performing drivers gives you a better performing machine.
Find out what brand of hardware the bits of your machine is made from. Then go direct to their official websites and look for the support section. You will almost always find they have drivers you can download.
For example, if you have nVidia graphics card, you will find the manufacture drivers at nvidia.com. Make must make sure you download the correct driver, as an incorrect one can completely cripple your machine.