Hdd space missing

i have read 4or 5 threads here on this and have tried solutions from here too,

i have an 80gb hdd (76.6gb) and i have 25gb of data on it but it is showing that i am using 48gb of data so i am missing around 20gb of free space.

i have system restore turned off
i have removed all previous versions
hidden files showing
checked the sizes of files in program files
checked for mal,spy,and other such nasties

now by doing this i managed to restore about 15gb of free space from a missing 35gb free space but i am still that 20gb short

im on vista ultimate, fully updated
8800gtx
asus a8nsli deluxe
2.5g ram
dual monitor
amd 64 4200 x2
80gb sata 72,000rpm 1024 days used

any help would be greatly apreciated

 

Try WinDirStat it should work on Vista. The bottom pane is a graphical representation of blocks that are proportionate to the amount of space a file is taking up. If you are missing 20gb it should help narrow down the folders that are taking up space.