Hi,
got it !
Not easy, I give my steps, not sure they were all necessary :
1. Create a disk recovery from another machine using the same windows version
2. Boot on with the infected laptop, and repair
3. When rebooting again, it failed another time. So, I access to the dos prompt and run Diskpart (don't ask me why I had this idea...)
4. The Windows volume, normally on C, was shift on D, and the partition was not "active" anymore. I reassign the letter and reactivate the partition as active.
5. Then reboot and it worked ! I've quicky ran adwcleaner that does some housekeeping, and everything seems now ok.
Thanks for your big help,
tihitibo