Hi,
First, I would like to thanks you for the help you could give to me.
So, it's now 3 days that I have seen that my processsor (Intel Core i7-3630QM 2.40Ghz) is stuck at 2.39Ghz.
My laptop is a MSI GT70 0NE, I bought it 6 month ago and the turbo boost technology was working, because the monitor was showing fluctuations between 2.4 and 3.1 Ghz.
But now, it doesn't go upon 2.40 Ghz !!! I tried a lot of things (Intel Processor Diagnostic Tool / Intel(R) Extreme Tuning Utility / My BIOS is up to date...)
I'm sure that Turbo boost is working but not as it should... Intel speed step is enabled (I tried to desactivate it but this doesn't help with the problem).
The only way to pass 2.40Ghz is to overclock the processor from 100Mhz to 105Mhz with Intel(R) Extreme Tuning Utility (which I could do only once, I don't know why I can't do it anymore... 
)
Could anyone please HELP ME ?? 
(I've got Windows 7 and I'm French if this can help)
THANKS 
EDIT:
I've just seen something which is really scaring me, in the system information window:
it's writen that my processor is a Intel Core i7-3630QM @ 2.40Ghz, 2394Mhz,2 core(s), 4 logical processor(s) instead of 4/8 !
HELP ME PLEASE !