pc slooowing dowwwnnn

My pc has slowly begun to slow down on it’s response times in opening applications and running programmes. I’ve checked for spyware, virus’, defragged, reinstalled (upgrade), msconfigged but no improvement at all. example WMPlayer repeatedly crashed repeatedly when opened, Firefox takes 1 minute plus to open, etc, etc. Would a reformat of harddrive and creation of partitions be worth doing? any advice greatfully received. Thanks