Thank you for your advice, Christophe!
Unfortunately, I'm not so skilled to follow it
So, I talked to the owner of the laptop, narrowed the scope and found everything in recovered files.
Laptop: ASUS X552W Hard drive: single Toshiba 1TB disk split into two logical disks C (system) and D. OS: Windows 8.1
Recently Task Manager showed 100% Disk utilization several times a day and at these moments all applications froze for several minutes. So, I ran "CHKDSK /f /r C:" to check the disk ...