ps once you install windows xp with the upgrades and update antivirus you can reconnect you old hard drive and scan for viruses and delete them it best to reinstall windows every 6 to 12 month to keep it clean and runnig fast unistalling program fragment your hard drive and leave scrap in windows registry, good luck

if you have never reinstall windows xp entirely you definetly have a system thas been compromise, best thing to do is get a separate new harddrive partition it in two or more part and install windows; before you do this download xp service pack 1 and 2 onto your new harddrive, reboot and disconnect the old drive and boot from the CD, this is the only way to bypass viruses and spyware that may detect you trying to clean the your computer, the reboot you suffer are cause by flaws windows xp has, and hacker design viruses and worm that attack those vulnerabilities. ps after you install windows xp ,install the service pack and antivirus before going conneting to the internet and disconect always when you plan to reinstall windows (unplug cable)