\. Thanks Neovex for the solution. I guess he is a Star Trek fan.

My problem is solved (Thank you my American friends who had the same problem as me: D)

For all those who have this problem and speaks French, I give here the solution:

1) Make a check disk: When you start your Mac press   + s
(To boot into “single user” opens a command window to full screen)

2) Wait until you‘ve finished registering Mac stuff and end type: fsck-yf
Repeat the fsck-yf until it is marked OK somewhere.
Then type exit to restart the Mac

3) Go to Application => Utilities => Disk Utility (Select Machintosh HD) and click “Repair disk permissions”

4) Last step, download and install the update to the backup system:http://support.apple.com/kb/DL1464

And it works! (Sorry for my English but I am Belgian and I speak French)

Link to my Soluton in French : http://forum.mac4ever.com/probleme-localiser-mon-mac-impossible-de-l-active-t695 82.html