confused where is my hard drive space

[skizzydizzychic]

we have recently purchased a quad 4 system with vista ultimate operating system and it works great never been so happy untill i noticed on a daily basis we lose between 3 and 7 gig of hard drive space, even if we install or delete anything it still disapears with no explanation, we do a defrag and disc cleanup weekly and sometimes we get it all back and sometimes we dont get back any at all, very confused to why this happens, is it the system rewriting itself or what plz help as i am losing my hair over this situation and cannot find any info for this problem
TREVOR

[erenoth2002]

This issue used to boggel my mind i even tried formatting the drive and the same problem continued to happen, it really bothered me....untill I started doing a regular full disc scan, it takes a little extra time but if i dont need my computer for awhile i schedule a full scan with bad sector recovery and mangically my gigabytes return and somtimes after a good defrag and disc scan (even at some times its wise to run a diagnostic from the bios) and Ill often get more gigabytes back than I expected.