The error messages I got from GParted and other software was
Input/Output Error during read on /dev/sda.
Failed to read SYSTEM.SAV
Another strange thing was that
smrtmontools said that it passed the health test!
So I tried to fix it with
ntfsfix but partition
sda3 had the command output:
Volume is corrupt. You should run chkdsk.
Now I'm stuck and I don't know how to run this command from Ubuntu.