CPU refuses to go above a certain level.

[calidar]

Had this computer for a few years now and it's been working fine, suddenly my CPU refuses to go above 1197 MHz.

I've got a Intel Core i7-620M @2.66GHz and uses Intel's turbo mode to go to 3.333GHz when it needs it.

Yesterday I cleared a load of dust out of my CPU's heatsink and downloaded a load of hardware monitoring software from CPUID.
Could I have done anything to cause this, or does anyone have any experience with something like this?

Any help would be appreciated.

Laptop is a Alienware m17x.

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[MindoverMaster]

Try turning off Intel's turbo mode in BIOS. Does it run at full potential?

 

[calidar]

Now running at 2.66GHz which is the cap without turbo. I'll restart with turbo and see if anything has changed.