I dunno what you have installed on that computer, but if it were me I would just wipe out the HD and reinstall Windows. Why waste time endlessly scanning your computer or rely on others' advice, half of which are useless? In addition, formatting your hard drive will cure your computer from 99% of all known ills, including virus, that exist on the market.
Here's an instruction on how to "clean install" Windows 7 or Vista:
http://pcsupport.about.com/od/operatingsystems/ss/windows-7-clean-install-part-1.htm
Here's an instruction on how to "clean install" Windows XP:
http://www.theeldergeek.com/clean_installation_of_windows_xp.htm
Good luck!
Here's an instruction on how to "clean install" Windows 7 or Vista:
http://pcsupport.about.com/od/operatingsystems/ss/windows-7-clean-install-part-1.htm
Here's an instruction on how to "clean install" Windows XP:
http://www.theeldergeek.com/clean_installation_of_windows_xp.htm
Good luck!