I found the solution to my problem :)
I traced the linux/slitaz startup-sequence to understand how it work sine I'm new to linux.
The problem is that certain Slitaz ISO files for a strange reason don't create some important folders when you try to install slitaz with the TazPanel.
So when you try to boot the system Slitaz try to find configuration files and those files are not created... in fact whole folders are missing that's why it default to terminal instead of graphical interface.
Here's the folders/files that are not created: /root/.config/slitaz/applications.conf
what could be done would be to create them manually but for me it was to much time consuming since I'm new to linux.
What I've done is to use another ISO image.
"GOOD" image/ISO = slitaz-4.0-loram-cdrom.iso
"BAD" image/ISO = slitaz-4.0-loram.iso
IMO I think the defective image/ISO have not been tested for "Installation" only tested to see if it's boot from USB/CD and it boot fine but don't install fine, so when you are a newbie like me it's confusing. ;-)
Hoping it will help you to have it run on your computer.
Thanks to everybody for the help ! :)