CPU clocked much slower than its listed speed

Here is the system I am using...

Dell Inspiron 5150 w/ Windows XP (SP2)
Pentium 4 3.2GHZ
768 MB RAM
40 GB hd, 6.8 GB free
ATI Mobility Radeon 9000 64MB graphics
Intel onboard sound

For a long time now, my system has been running extremely slow. When my warranty with Dell was still good, I had them replace the HD (it had a seperate problem), the memory, and the cpu. Nothing really was fixed. I have friends with almost identical setups, just without the upgraded graphics card (XGI 32 MB comes standard), and semi-graphic intensive programs are running MUCH faster on their computers than on mine. I have defragged, run every spyware program that is legit (my hijackthis log is clean, and adaware, spybot, and spyware blaster come up empty, among others). I also have Symantec Anti-Virus, nothing there. Still running VERY slowly. Rollercoaster Tycoon 3, which is supposed to run best with ATI cards is even very choppy with the most slim graphics settings. So, I downloaded ASTRA32 to just make sure everything was doing what it was supposed to, and it read a clocked speed of 1595.3 MHz. First of all, is this probably the root of my problems? Is there anything I can do to fix it, or is the chip physically damaged?

Thanks for any help!

 

I use Everest to check my clock speed.

Also, norton antivirus (I guess it's symantec) sucks, get Avast!. (more things get by norton than Internet Explorer >_>)

 

I just ran Everest as well, and it's giving me about the same: about 1593 MHz. I think the HT might be screwing the diagnostic programs up. In some places it says 3.2 GHz processor, and in others it says Northwood Hyperthread 1600 MHz. Maybe the clock speed isn't my problem? If so what could it be?

 

Well I have determined (I think) that the problem is the thermal throttle. The computer had overheated before either because the fan was clogged, or it is bad. The fan never comes on now, because the computer is never getting hot enough. How do I reverse the thermal throttle? I ordered a new system fan, btw, in case it is the problem. Will the problem fix itself if a good fan is put in?