Windows can be clotted up due to data accumulated over time. Applications can store data over the hard drive and fragment the hard drive. When windows relaunches the application another time, it locates this fragments and sorts them, then launches the application.
Fragmenting can result in slower application startup, since it takes time to locate these data fragments. One way to solve this is using a defragmenter.
Windows has a defragmenter found in Start > All Programs > Accessories > System Tools > Disk Defragmenter
However, I do not recommend this method as it takes an extremely long time for windows to defragment the harddisk.
One software I recommend is Auslogics Disk Defrag available for free on the web
It does defragmentation very quickly and takes less than 30 minutes for a full defrag.
There's also a summary to summarise the increase in computer's speed.
Another way to speed up windows is to regularly clear Junk files, Temp. Internet files and other unneeded files.
Using the application CCleaner, or Crap Cleaner, available at
It helps optimize your system, clear private data and cleans the harddisk for free.
Below is CCleaner's introduction.
CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. Additionally it contains a fully featured registry cleaner. But the best part is that it's fast (normally taking less than a second to run) and contains NO Spyware or Adware! :)
Another way to speed up the system is to uninstall heavy unneeded programs which use plenty of disk space when you do not use. This clots the system and it takes a longer time for the system to find the needed files for application. Use add and remove programs utility to safely remove the program, then go to Start > My Computer > C:\ > Program Files and delete the folder containing the program. Never delete the folder without uninstalling the program.
Try using antiviruses which do not use up a lot of system resources.
ESET Nod32 antivirus is what I am using, it has a smart technology to passively scan viruses without using much system resources. Try to avoid Norton as it usually slows down the computer.
If possible, remove the desktop wallpaper for faster loading.
Registry defragmenting may help too. Try finding a registry defragmenter online and occasionally defrag your registry.
Lastly, using msconfig Start > Run > 'msconfig' (without quotes)
Uncheck programs not needed during startup like Photoshop etc. This does wonders to your start up time.