All source files are deleted

Can somebody please help?

I started an incremental backup from 2 folders to an external drive. There was 20gig data. Now when I check them. All files on the source are deleted and there is no back-up on the target disk?

Edit: The problem is fixed. Apparently during the back-up, Comodo somehow deleted my register on my source hard drive. So it did not deleted the files themselves, just their allocation. I used a data recovery tool and it found all my files and I had to recover them using this.