Jemand

 sudo mount /dev/sda3 /media/sda3test/
Unexpected clusters per mft record (-1).
Failed to mount '/dev/sda3': Invalid argument
The device '/dev/sda3' doesn't have a valid NTFS.
Maybe you selected the wrong device? Or the whole disk instead of a
partition (e.g. /dev/hda, not /dev/hda1)? Or the other way around?