I assume that your video is on the MOBO. You might try using a PCI or PCIe video card and see if you can reclaim some ram.i entered in BIOS and i didn't see anything about ram shared. I only can read: Ram memory: 4096 Mb
eh i solved the problem!
i just have to update the bios! and i have know 3,75 usable. Thank you for your help