Alleged backup failure although TIB file size ok

Whenever I am using ATI 2015 I boot from DVD and start the backup manually. I did so the other day with the aim to backup a notebook's OS partition after successful upgrade from Win 7 Pro to Win 10 Pro. At the end of the ATI backup (with the 'validation' option ticked) the message popped up 'Backup fehlgeschlagen' = backup failure. I repeated the backup producing another TIB file with different file name and of (almost) identical size. The size of the 2 TIB files were resaonable so I did not take the failure warning seriously, which I now very much regret.

Instead, not knowing how mad I must have been at that point in time but - believe it or not - I took the 1st of the 2 'corrupt' TIB files and tried to restore it on the notebook, with the aim to prove validity of the backup !!!! This decision was based on the strong belief ATI can't be wrong. I never had backup or restore failures, ATI always worked properly and reliably since I am using it (for more than 10 years now). I was really naive to jeorpadise the fresh Win 10 installation.

Now, the status is that the notebook does not boot any longer. One thing is strange though: restoring a definitely validated Win 7 backup also failed. Any idea what to do now? Is there a way to at least restore the last intact Win 7 Pro backup (i.e. the one made before upgrading to Win 10)?

Thanks in advance for helping a real stupid lad ;-)
Regards, Scholli