Cpu 100% Usage

For the past 2 days my computer been extremely slow it seems that any application i run it'l make my cpu flatline at 100%. My comp is even slow on initial windows start up, boot is like 10min. and log in is like 5 min. Can someone help. Thanks.

Heres the list of things i've tried:

1.Using virus/spyware scanner to look for anything suspicious.
2.Tried disabling programs thru msconfig.
3.Tried checking registrys for anything suspicious.
4.Tried checking while in safe mode.
5.Tried reformatting my main sata drive and reloading windows since i only have one drive.
6.Tried reformatting another new ide drive and loading windows on that.
7.Tried switching old ide/sata cables and using new ones.
8.Tried using memtest.
9.Checked all the wires in my computer to see if everthing is hooked up.
My comp runs so slow it took me like a whole day just to install winXP on either drives.

Heres the list of things i think that could be wrong:
1. 2 of my drives(IDE,SATA) could be screwed up wich i doubt because its like 3 to 6 month old.
2. winXP disc could be scratch wich i doubt because it is also brand new and there is no noticable scratches.
3. mobo could be faulty wich i doubt because its brand new.
4. psu because the led light went out for no apparent reason but it is also brand new.
5. rom drives could be faulty but both of um are brand new.
My comp is fairly new
amd fx-53
2gb ocz
asus a8n premium
550 psu
1 wd 10000rpm in sata
bfg 7800 gtx
x-fi extreme music

 

The 3 points above lead me to believe you have a hardware issue. Fresh reloads of XP taking all day instead of 30 minutes is a big red flag. You've eliminated drives & cables. I assume the memcheck came up OK (you didn't specify), so your RAM seems good. It's difficult to say without having parts to swap out as I've seen this problem caused by processor, mobo, power supply, even video card.

If you have onboard video, try that instead of the video card to try & eliminate things. If that doesn't work, you're looking at one of the other components being bad. Doesn't really matter how new they are, electronics break all the time. That's why manufacturers have to offer a warranty of some type. Also doesn't matter if it worked fine one moment, then suddenly didn't...the nature of electronics is generally instant failure, not a slow degradation.

Good luck with pinpointing the problem(s).