thanks for the reply.
so did I this morning but without success.
still the same display issue.
I've booted in safe mode, uninstall the intel graphic driver, reinstall the chipset and checked the alst bios version (all is ok). then reinstalled the latest version of the intel graphis driver (downloaded freshly) and after reboot, back to the previous state.
any other recommendation ?
finlay it was the RAM.
I've changed it with another one from my stock and it works.
so RAM could be an issue there.
thanks for your help.