I know this might not be helpful.. but umm.. have you tried nit using windows?
Since the PC shows the full 16gb it must be registering it. So something inside windows must be occupying the rest of the space.
I've seen windows alone go up to 4+ GB so the ~8GB your missing here aren't unrealistic depending on what programs are running in the background.
Ballistol öl, einfach überall drauf schmieren, ist wie WD40 nur Lebensmittelecht und nicht so chemisch