If like me you want to give some new energies to your macbook and install some memory and a new SSD hard drive. Be ware of this : you Crucial SSD must be initialized before install El Capitan on it.
I have tested my drive, connectics, … and finally found this URL pointer : http://forum.crucial.com/t5/Crucial-SSDs/How-to-initialize-your-SSD-Mac/ta-p/111490