Thinkpad t40 harddrive space issue

[annon]

my t40 is not reading the 40GB hard drive right. It recognizes that only 500Mb space is left, but when I select all the files and folders in my C drive, while having Hidden Files enabled, it shows only 18GB used. i know there is a hidden partition on the drive but it should take up only around 5Gb of the 40GB drive. i don't now if there is system back up going on the same drive that has taking all that space.Well, If any one has any suggetions about how to recover the lost space, please help!