My Hard drive was fitted approx' 2years ago. the size is 30gb. having an ancient Pc I have never used more than a quarter of its capacity... leaving my AVG anti virus programme running a system check one evening ,i went off for dinner. I returned to be told all was fine... The next time i checked my C drive the capacity had completely reverserved itself... I now have 3/4 of my hdd full rather than empty... What the hell's going on?