hmm we need some help from you to see what is wrong, likely it is NOT missing but is just a extended partition with the rest under it.
if you open a console (screenlike icon at bottom of screen) and type
Code:
sudo fdisk -l
and hit enter what does that output? what does the comand mount say?
Code:
mount
what does dmesg say about your disks?
Code:
dmesg|grep hd