I also have a Dell laptop (Studio 1458), and I am also experiencing the same issue.

In diskpart, I did notice that the main volume file system got corrupted into just RAW type, no longer NTFS. I think that if I can convert it back to NTFS, I may be able to recover my data.

In the Advanced Recovery mode, there is a way to launch command prompt.

Once command prompt is launched, type the following

diskpart

list volume

If you see any partition as RAW, we have an issue with data integrity

Update:

Well, I wish there are easy ways out there to fix the partitions. As it currently stands, I have to somehow extracting Windows.old from the RAW partition, and go back to Windows 7. While this may not be a bug on Microsoft part (may be hardware?), Windows 7 used to work just fine, so I can't help wondering if there is some edge case where Windows 10 can corrupt NTFS into RAW.

Dell seems to have partition layout like this

Partition 0 as the bootable system partition (as defined by Microsoft)

Partition 1 as the primary partition (has Windows on it, but is now of RAW format)

Partition 2 as the OEM reserve partition (presume this has to do with Dell)

I wonder if partition 2 is the reason to confuse Windows 10. Alternatively, Windows 10 may want a Partition 0 to be of 500Mb, it had to push back Partition 1 to make some space; hence, messed up Partition 1 in the process.



Update2:

I managed to recover Windows.old using Active UNDELETE (not freeware unfortunately) inside Windows PE (you can build your own PE environment or pick one off the Internet. I used gandalf windows 8 pe). Maybe someone will have better luck with Recuva (freeware)

I am just going go ahead and install fresh Windows 7 on the Dell (not using the OEM disc, but of retail disc), and upgrade to Windows 8 that way.

Update3:

Yep, no go. Even with a fresh copy of Windows 7, Windows 10 fails to upgrade. I think we have a real bug here in Windows 10. Dell web site did say that they don't support Windows 10 on Studio 1458...so this is a real bummer here