In Materials Studio if calculation gets failed it asked for the options that you want to see the file or not. If you opt no it will directly remove those files from your project.
If some files are not saved you can’t open then it will show the empty document.
Which version of Materials Studio are you using?
For more technical query you can also use Materials Studio Community
Thank you Mr. Chawla, after re-starting and clearing the left temporary files on the Project folder (and after several re-start) it's working now. Kind regards, Avni