I finally got the solution by opening completely the laptop and unplug the CMOS battery (which lead to a 'reboot of the bios') and then I could directly access to the bios and REMOVE the UEFI option (in 'advanced options') then the laptop could start again properly on the HDD. The problem came from the new installation that I made. It was without 'UEFI' which causes problem when the computer wanted to load the OS on the HDD. Apparently you can set-up a USB key with 'UEFI' option to make it works properly. I hope this will help someone!
With windows 8.1 preinstalled on a L55-B Toshiba laptop, to get into bios when the pc is powered off, need to have done a shift+shutdown with windows 8.1 up so does not use fast boot during the next boot. Nov 4, 2013 - The Toshiba Hardware utility (HWSetup) can also be used to. This method may be the only way to access the BIOS settings on some laptops.