Check by doing a right click on the disk under properties to see what size it is and how much of the disk is occupied. It may also be that your have the OS configured to not show hidden or system files. You restore point data will be such and can occupy lots of space. Check whether your partition is NTFS or FAT-32. If it's FAT-32, you will only have 32 gigs available. Hope that helps.
i have to harddrive's an 80 gig as the master and a 200 gig as the slave, the 80 is for the os and the slave for my downling, the 80 gig is full, not sure why when i check all the files and folder's it only adds up 12.2 gig.
please help, this is realy odd, system restore has been turn'd of and i have run disk clean up and got rid of my game's and still it's full.