Current processors will throttle themselves back to lower power consumption and heat. Given the need for the CPU to use all its cores, then the additional cores will turn on. For instance, when not setup to run on all 4 cores, my processor would normally run off of 2. Most common programs will not have a high need to run current processors @ 100%. Another example would be that when I am playing WoW or Sw:tor, I utilize at most, 15-25% of my processor. I7-920 @ 3.8ghz. Hope this helps. Some additional information about your processor might also help if this is not the case of your processor. If you want to ensure that your processor is running correctly, programs like Pime95 or CPU-iz, and Speedfan will show your hardware usage. Good Luck!
so basically, if the processor gets heated up, it just underclocks automatically?
and I forgot to mention my motherboard, I'm not sure if its compatible but heres the info.
Manufacturer ASUSTek Computer INC.
Model Basswood (Socket 775)
Chipset Vendor Intel
Chipset Model P965/G965
Chipset Revision C2
Southbridge Vendor Intel
Southbridge Model 82801HH (ICH8DH)
Southbridge Revision B0
Not quite what aviconus is getting at. Thermal throttling (when the CPU overheats) and Speed Step (where the CPU downclocks when idle) are two different things. Thermal throttling tends to occur when the CPU cooling isn't sufficient, but isn't what you're seeing in your case. You're seeing your CPU automatically reduce its frequency when it's not being fully utilised to save power...it's a normal feature.
Download CPU-Z and Prime95, as aviconus said. Load up CPU-Z and you'll see the CPU frequency changing. Now load up Prime95 and run a stress test, and you'll see your CPU usage shoot up (as well as the temps...use CoreTemp to see that).
You can also check your BIOS to see what speed the CPU is running at.