Temporary, log, hibernation, backup, Internet browser cache also eat up free space quickly. The most possible reason is that C drive is filling up by many types of junk and unnecessary files. In previous Windows Vista and Windows 7, some people feedback such issue that C drive usage percentage is showing incorrect, but in Windows 10 this problem seems to be solved, however, it is still a possible reason. If C drive has plenty of free space but it becomes full in a short time, you'd better run your anti-virus software to scan.
If the computer was attacked by some particular virus, large amount of files will be copied or generated. Windows 10 low storage space maybe caused by 3 kinds of reasons including: Why Windows 10 runs low disk space on C drive
