Hi
Its not a 70 gb its an 80 ...
But Windows cannot count properly anyway lol
500 is peanuts, dont worry about it as long as you have no FOUND folders in your C drive (you need to turn on HIDDEN and SYSTEM files to see them sometimes)
IF you have your hard drive is failing... if so run a HIRENS CD full hard drive test on it...if it fails that, NEW hard drive time...
All the best Brett