j'ai trouvé la solution sur le fofo englais de steam
j'ai trouvé ça
1) Run the downloaded "installer" (the one that kept loading to 100% and crashing)
2) Look in c:\Users\(username)\AppData\Local\Temp
3) Find a directory similar to "I1427247224" with a date and time of when you did step 1
4) Inside that directory go to InstallerData/Disk1/InstData - you will see a compressed file called "Resource1"
5) Inside "Resource1" go to $IA_PROJECT_DIR$/src_path
6) Copy the folder "Launcher" to a drive and location you can get to (Probably your c:/ drive)
7) Inside "Launcher", execute "Bethesda.net_Launcher"
8) The "Launcher" will update and restart.
9) Once the "Launcher" is running again, click the INSTALL button.
10) Wait for the launcher outside of Steam to finish installing/downloading/patching all the updates
11) Go into the Steam launcher and have it once again download all the files through the Steam launcher
Ceux qui ne sont pas sur steam oublié la 11ieme étape