* How do you know that you CPU is 2.4GHz?
* Have you checked your system documentation?
* Is this a brand product or is it a collection of OEM parts?
* Have you checked your BIOS settings to see that the CPU frequency is adjustable the hard way?
The way you phrase the question suggests that you're not very knowledgeable on the subject, so I'm inclined to count off the possibility that you built this system.
P4 suggests that this is a new system, so you could perhaps talk to the shop from which you bought it?
Good luck,
Engin