I have a windows 7 system having a c drive partition of 52 GB. It shows 7 GB free disk space but all the folders(including hidden files n folders) on the drive total upto 27 GB. Plus i guess that my disk space is decreasing regularly. So wheres my missing 18 GB?
Unless you disable them, the hibernation, system restore, and paging files can consume that much space easily. If it is an SSD turn off hibernation and think about turning off system restore, also flush all the old restore points or at least allow it less drive space. Move the paging file to a HDD instead.