Reset laptop to factory settings and backed up my files to an external drive with Dell SupportAssist but no access to backed up files

Hi Everyone

I've read through countless threads and tried all the solutions I could find but none worked. A few days ago, I had to restore my laptop to factory settings b/c I kept getting the blue screen of death.

I used Dell SupportAssist to back up my files to an external hard drive and it looked like the backup succeeded. However, when I tried to extract the z files (see screenshot), I got an empty archive, despite the fact that the z files total about 600 GB. What am I doing wrong?

I tried 7Zip and WinRAR to no avail, the extracted folder is empty.

Your help would be much appreciated!