Yesterday I've had 2GB of free space on C and only after using Blender it has all gone. Can anyone help me?
Your problem is not neccesarily related to Blender. Just because it's the only thing you used doesn't mean it's the only thing that happened on your PC. Yestarday I had 30GB of free space on C and after only using Blender it went down to 7GB. Well actually turns out Windows downloaded update files in the background.
It will scan your PC for any temporary old files that could be taking up space and let you choose to remove them. If that doesn't solve your issue than your best bet is to just go over your C Drive manually and cleanit up your self, remove any unwanted files etc.
Remember that your Desktop and any files in the recycling bin are also a part of your C drive, so if you're saving a lot of things on your desktop it could be taking up a good amount of space.
I reccomend WinDirStat for browsing your drives and doing manual clean up, it will make it a lot easier to identify areas with large files or folders that take up a lot of space.