More Problems.....

For some reason, when my HD hit 55 gigs, my comp hit the fan and slowed down a lot, there are no viruses Detected from norton or Micro trend, though I did come across 5 trojans and got rid of.... This bloody thing is running terrible, my specs are in sig..... I'm thinking the graphics is getting even worse and pulling it down or something else maybe? Help would be grateful! Cheers, Gunny