Windows 7: Free system disk space going out by itself

Hi forum! Thanks for your help!
I am having this free disk space problem that I'd like to understand. The message appeared quite some time ago. I had my thunderbird profile in the C disk, as well as some data. So, I moved it and deleted other stuff, and got myself bright beautiful blank space on the C, around 7gbs.-
Thing is it was a month ago or so, and now, the problem appears again. So, I am asking for a kind of solution, but in first place, I'd like to kwon what's going on.-
I have downloaded quite a few things, but they are in another partition. I always wipe off the temporal files, as well as internet temporary files. If I install programs, they are in another partitio too, but is not the case, for I have not installed almost anything(I know that even if we put the 'program' in a partition, some data goes in C nevertheless).-
I am aware of the existance of those progs that will show the ammount of data and its location and stuff. I have read mostly how to get rid of useless things, but I'd like to know what happens, and if I can prevent it from occuring.-
I have seen so far, with one of those that show the data, that the same archive can be located in both folders. That happened with the thunderbird profile files, which 1 gb would be 2 gb of disk allocation.-

Thanks again, and be well!

Hey!
Update:
I didn't do a thing, and I have now 3,5 GB of free space, out of nowhere. Any ideas?

I'm not sure of the question. Are you asking about what Thunderbird does or what Windows does when you install a program? Or.....????? Please be specific.

You really need to use "one of those programs that will show the ammount of data and its location and stuff".

I'd recommend Treesize Free

See what it tells you about where the space is being used.

Also, how big is the boot partition? Can you post a screen capture of a full screen Disk Management window.

Hey! Thanks for your answers.-
I am not interested in thunderbird, I just named it, my mistake. What I want to know is how windows manages the free space, and the reason for having lost about 7 gb of free space when I didn't do anything on it. I know how to erase things, and I have quite a few of those programs(thanks for suggesting one, I didn't know it). But I am not up to it.-
I mentioned thunderbird for it has quite large archives, and, I saw them duplicated. But the same happend with other files, I don't remember their names, they where .msi I guess(Install packages).-

So, I'll try to be specific:
1) How does windows manage free space?
2) What can I do to prevent it from using all the free space?
3) What happens when some free space comes back by itself?
As I said before, I had 3,5 GB(around 7 PM), and now(10 pm) I have 2,93 GB, and did not do anything, neither insalled a program, nor downloaded any file. I did not even entered web sites. I have been just listening to some music, and was no infront the computer.-
4) I am not willing to use the treesize kind of program in first place, for I am not trying to free space and get it lost again. Might I be a noob, apologies if that's the case, but I want the free space to stopo being consumed, not just erase things.-

Thanks!

Ummm, without detailed information from a utility such as Treesize, members really can't assist you.
TreeSize Free tells you where precious disk space has gone.

Hi again, this thread shows quite my question:
Hard drive free space fluctuation...?
I'll consider downloading that tool the, thanks!
Remember I'd like to prevent the problem, i.e. free space going from 7 gb to 100 MB, back to 3,5 GB, again to 200 MB and so.-
And I'd like to add that the hybernation file is disabled, and the pagefile is in another partition.-

We would also have to know what's running on your system. Windows isn't causing the problem. You obviously have software (or malware) running in the background using disk space. Start Windows Resource Monitor and click on the Disk tab. This will show you all processes using disk and what files are in use.

We can't see your system for here so speculating on what is using the disk is just a guess.

What program and/or method are you seeing free space change?

You say you are jumping from 200 MB to 3.5 GB

Pure speculation as stated already but - check your settings for system restore on all drives. If a restore point gets created it can use a ton of space with no obvious signs of activity.

Other than that it is possible to install yet more software to monitor directories. Here's screenshots from my machine running a couple of apps that run without installation and can monitor file changes.