Computer Very Slow (what's wrong?)

Hi guys!

Over the past couple days I've been trying to fix my Dell XPS M1210 Laptop.

Specs:
2.33Ghz C2D 4GB Ram 100GB 7400rpm 7400 GeForce Go.... anywho...

The problem that I'm having is that it's running extremely slow. I tried reinstalling windows xp (something that normally takes me less than an hour to do) and it's taking me over 6 hours to install!!! The problem is not just the xp installation, that's just an example. When I get into xp it's still really slow.

I've tried these things already to fix the problem:

Replaced the hard drive

Replaced the ram

Replaced the DVD drive

Used a different XP installation disk........

What else can it be? CPU? Motherboard? Fans? Overheating?

Thanks for your help!!!