Many computers take a lot of time to boot (or start ).This is due to many reasons.

Some slight changes can do wonders for your system:

1. Press start->run then type msconfig and press enter.

Go to the startup tab. Here you will see a list of startup items. These are all the programs that automatically start when you boot your PC. It is these that slow down the boot up process.
                                 So uncheck all the unwanted items like ms-office, messengers other utilities that u may not need at startup). Don't uncheck your antivirus software.

Restart your Pc to and see for yourself, your pc will now boot faster....  
    
2. A great new feature in Microsoft Windows XP is the ability to do a boot defragment. This places all boot files next to each other on the disk to allow for faster booting. By default this option is enabled, but on some systems it is not, so below is the information on how to turn it on:

Go to Start Menu and Click Run
Type in regedit then click ok
Find "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Dfrg\BootOpt imizeFunction"
Select "Enable" from the list on the right
Right on it and select "Modify"
Change the value to Y .
Reboot your Pc and see the change yourself.
 
3.SPEED UP BOOT BY DISABLING UNUSED PORTS.!!
You may have tried many tweaks like modifying windows XP start-up applications, prefetches, unload DLLs method, etc. And yes those methods do work for me.
                    I have just accidentally found out another way to give you an extra boost in windows XP's boot performance. This is done by disabling your unused devices in Device Manager. for example, if you don't have input devices that are connected to one of your USB's or COM ports, disabling them will give you an extra performance boost in booting. Go to Control Panel -> System -> Hardware tab -> device manager Disable devices that you don't use for your PC and then restart.

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