Compaq Presario has suddenly gotten sluggish

I have a Compaq Presario R3240US which is 3 years old. It runs XP Home, has 512mb RAM, and a 60 Gig Hard Drive. The processor is AMD Athlon 64 3200. It takes now about 5 mins. to boot up, and Windows IE7 often freezes. It is a computer I inherited, and I understand that it was never turned off by its previous owner. Any suggestions?