What happened to my computer hardware? plz help?

[Steel-Rain]

Ive got a home made system so let me show u whats in da box:
mother board:
ASUS A8N-SLI
- it holds 4 gigs of ram
-sockect 939
-gas cooled=D
processor:
AMD 64 BIT:
single core
bout 1.8ghz i think if not more
RAM:
1 GIG
hard drive:
-120 GIG
-SATA
graphics card:
ati readeon saphire 128 mb

Back in 2004 this thing was lightning i could have 15 programs running like nothing counter strike being one of them. the probelms started when i started download garbage on to it like limewire and share ware and free ware programs. i had a problem once and i had to format the thing and one hard drive went curupt. when i installed windows again the speed upon start up was horrible. my processor is always running at around 100% which was uncommon before and my ram is reconized but i think its curupt 2 or just gave in. to put in a question form how can i make my computer kick butt again or should i build a new one?
by the way i got 39 programs running rite now..
thanks