I've been having this problem for some time now but I never had a clue about it. My C directory, which is quite filled (about 10Mb left...) keeps changing the free space that is left. It goes from 10mb to 6Mb in one second while I am not doing anything. And even when I'm trying to free some space, it still goes down. Is this a virus? And if it isn't, what can I do?
Its probably your swap file or some other system files being changed in the background. Completely normal
Not exactly related to your question, but to help with your space problem, I'd strongly reccomend running a disk defragmentation.
You're operating with 10 megs left. Ah, free up some space! I'd recommend at LEAST having 100mb free.