I solved it !!!
Step I did (I was on linux so I saw all partitions):
- Take SDcard from Kobo (open the back and take it)
- Put original rcS file in partition "rootfs" (etc/init.d/rcS)
- Removed files copied when upgrading with KoboRoot.tgz file
- Switch on
AND PIXIE FACE ON THE SCREEN !!
I did a factory reset via menu & a backup, just in case :P
Thx all of you guys for helping me out !
(I added karma point
)