You don't understand, a PC game like Witcher 2 is nothing like an emulator. Witcher 2 uses your GPU, which will make the computer very hot considering how much they tend to vent out. Dolphin will mostly use your CPU; which may not be as hot to you, but once it reaches a certain temperature, your PC will start throttling the CPU speeds.
Yes I understand but I admit it was a bad example. The fact is that with the same processor, other users just run fine ! My problem is that my processor shut down to 1.2 GhZ even if its temperature is 60° :/, that's what I don't understand. When it stays even at 2.4Ghz games run fine but sadly it stays like this just some seconds.
Hmm, if even plugged to power and without overheat you can't get to a steady 3.2GHz, something is really wrong. Verify your OS, you may have some OEM program doing this. Check also your power supply, it may be faulty, IDK...
Have you tried using ThrottleStop? It can help force your CPU to a higher speed if there's some incorrect throttling going on.