PC Problem running really slooow

I just recently reinstalled WIN xp sp2 and formatted my hard drive. I usually do this once a year for a good clean out. Anyway, this time it was all good for a week or so but then everything seemed to start going really SLOW!! I mean when you click on (anything really) my computer for instance, it can take a minimum of 50 seconds to open that folder and show the contents. Once its open when you click on the next icon (C drive) for instance, it will take another 50 sec - 2 min to open that...and so on. I have done all the antivirus and malware removal with no findings at all. My Sound card was very old so I bought a new one and installed it but that made no difference. I installed a new processor and that has made no difference. Everything works, its just really slow and I dont know what else to change.
The system is
P4 3.2 GHz
XP SP2
2 GB RAM
N Videa 6800GT
Creative SB 5.1 VX

Any ideas???

 

Sorry. I forgot to add that I have also installed a new HDD. It made no difference.

 

Hi

Do you have onboard video on your motherboard? If so, try removing the video card and using onboard video to see if that makes a difference (to rule out your graphics card).

If that makes no difference, try the RAM dance:

(use these steps to troubleshoot your RAM)

Boot with only one stick of RAM in (first slot)
Exchange the RAM sticks, using the second stick of RAM in the first slot
If both of those steps check out, switch the RAM modules (use second stick in first slot, first stick in second slot)

You can also use Memtest86 to test your RAM (slow real-time performance leads me to believe your RAM or your motherboard RAM slots could have a fault).

 

OK. Checked the video card and can rule that out. Ran the memtest software and no errors there either.
Anymore suggestions?