I have a Sony Xperia S. I'm trying to update it from the SonyPC Companion. I get as far as the Prepare phone stage. I follow the instructions, disconnecting USB and phone from computer. I turn off my phone (it has 100% battery). I then reconnect the USB and hol dthe volume down key and reconnect my phone. NOTHING HAPPENS after this..I can get no further...PLEASE HELP!