if after cleaning the system of spywares virus and startup programs the system continues slow check this:
first of all look at the mainborad.does it have an amr slot?remove anything connected to it,these nasty cards can really slow down a pc,replace it by a "real" card if possible.look for a bios update,if you cant find it then clear the cmos and reconfigure it.check te hard drive cables to see if they have 40 or 80 wires.check the cpu temperature.install the most recent drivers from the manufacturers site.do not install softmodems.if you have a celeron you can try to overclock it but whatch the temperature.