8 gb Memory vanished from 40gigs

In my computer i am having p3 intel motherboard and i am using seagate 40 gb harddrive but i can’t get 40 gb whole detected it only detects around 32, i tried some sofwares but not working out is there any other idea except bios pgradation which may work…
have four partition
c:6.**gb
d:12.**gb
e:8.**gb
fourth linux :2.5gb
swap space:1.5gb