MohammedSF wroteTry the normal boot option in the bios "not a fast boot option" and see how much ram the bios checks during post.
or use a bootable memtest to check your ram.
if it's 4GB then it's OS related, if it's 800MB it's a hardware problem, if you have free so-dimm slots, cut the power line of the built-in rams and use external sticks.
the system state it has 4 GB but only 800 MB usable .
I will try to check them with memtest