Uninstall all unused programs. Run ‘msconfig’ from the Run box. On the start up tab, uncheck everything. Remove all the items from the start up folder in your start menu. Also, use task manager to determine any resource hogs you can remove or services you can disable (like Ipod service, spooler if you’ve no printers). Got to services, go to the properties and change start up type to disabled.
You can rebuild XP with all your settings by booting off the cd and selecting install windows then repair installation. However if your resource hog is still installed you won’t improve things. This takes about an hour or so.
Also, the more mail in your inbox the slower your mail program to open mail. Empty your deleted items, delete all old email.
There are many possible reasons that your computer system runs slower than before. There might a virus infection on your system that is continuously running on the background. The very first thing you have to do is to backup all your important data and files before any viruses could proliferate and completely paralyze the entire system. Then, run a full system scan using your latest and updated antivirus software.