First find out what files in what folders are causing this. The program from http://www.jam-software.com/treesize_free/ will help.
Then try to find out what program does this. The program from http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx will help.
Then post back your findings.
I have been experiencing a rapid but temporary loss of hard drive space. About 400GB are free when computer turned on however this free space declines at a rate of about 50 - 60GB per hour untill space runs out and the computer stops working. The free space is restored upon a restart. Computer is a HP running Vista with updated Norton 360 protection software. Any ideas on what is happening?