Disk space in Win2kserver

i have win2k server . on which i got 36GB hard disk. an this disk am seeing free space of only 1.6GB & the there are only 4 folders in this drive which is totally about 6GB. so out of 36GB 6GB is used & 1.6Gb is free . where is the rest of the disk space gone ? i tried rebooting & checked hidden files. no luck ..