@nouvel,Martial, I do not own this phone so did a search to see what I could find that may help. You did not state your phone model. Information from the 1st link below may help if not perhaps a factory reset may have to be done 2nd link. You can also do a search, if reset not for your model, normally fairly generic. WARNING !, Hard Reset will erase all of your data.
Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
http://www.tomsguide.com/forum/id-2747130/android-tablet-accidently-disabled-keyboard-put-password-tablet.html
http://www.hardreset.info/devices/blu/blu-studio-50/