HD space lost

[beppecet]

Hi there, my system (Windows 10 Prof) gets a reduced space on HD on the system disk (C. I've nstalled a new one increasing the capacity.
The first day the free space was 256 GB on 513 of total space; after one day the space was reduced to 139 GB; Today the space is about 18 GB?!?
I didn't install any new program and I didn't download anything.
The Antivirus Program (Kaspersky) doesn't detect virus or malware, The HD check (chkdsk) doesn't detect any problem.
Has somebody any ideas regarding this problem?
Thanks

 

[beppecet]

FIXED
I found the solution.
It was the transactions log file of a SQL database whith a no limits dimension and a full recovery property (my error).
After the correction I've recovered all the space on the disk.
Thanks for Your attention
Beppe