I don't think it's in Windows.old. That contains just what Windows needs to go back to 8.1. But it might be in your profile inside Users inside that folder. Did you look?
If not found that way, just go and search for one of those old files on the whole hard dis and - if it's still present - you'll find it. Using a wild card (like *.mp3) in the command prompt is the easy way, if you know the right commands. Otherwise use the GUI (File Explorer) to search all over the hard disk.
If not found at all, restore from your backup. That shouldn't be necessary, however.
Kees
PS. it helps to know the difference between file and folder; ntuser.dat is just a file (part of the registry); it's not a folder, so it doesn't contain other files. And if you look at the size (less than a few MB), you know it isn't a video, because those are much larger.
Kees
I just upgraded to Windows 10 from Windows 8.1. I can see all my files must still be on my harddrive as my harddrive hasn't gained any extra space. However, when I go to the C:drive Windows.old I cannot locate my old files. I'm pretty pissed as i had a massive collection of music and video and want them all back. Am I missing something or looking in the wrong place? Inside Windows.old I have the following files Perflogs, Program Files, Program files (x86), Recovery, Users, WINDOWS. There is a file NTUSER.DAT.gu in the Windows.old-Users-Guest could all my files be in there? Any advice and or help would be much appreciated

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic