Plz Help having trouble

my cpu usage keep spiking to 100% or will start out little and keep increasing increasing and then dcrease rapidly i havea dual core intel chip and 1.5 gigs of ram and a 512 vid card i just reformatted and now my comp uses up way to much cpu when i look at the readings on the cpu usage chart the lines are out of wack for both processors id apprechiate any help