memory problem

my c drive memory keeps on lowering without saving anything can anyone help me?

 

First thing-:without action, nothing happens on the computer....its just a machine
Reasons that hog HDD space without knowing:
1]Virtual memory space
2]system restore space
3]hibernation save file space(hibenate.sys or something like that)
4]registry might not be cleaned for long...unwanted registries
5]MS office setup files till stored
6] Lot of data still in Recycle bin
7] Internet temporary files storage not cleared for long

Thats all i can think of right now....some1 wil surely add m9ore to this

BTW, there is no reason to post the same problem in two different forums.