Dell 5175 - stuck on black screen after "Preparing Automatic Repair" or USB boot

Hi all, 

I can't quite figure out what is going on here. 

The tablet froze completely on the Windows 10 log in page, before going for a blue screen (I can't remember the error name - didn't think it was going to be a major issue). 
After reboot, it went to a screen with "Preparing Automatic Repair" and the screen went black (lit, but with nothing on it, that is). It can stay there 12hrs at least, doesn't change a thing. 

I ran the onboard diagnostics: no isse with anything. 

I tried booting from a USB created with Windows Media Creation tool - same black screen. 

Memtest86+ (ran for 8 passes) doesn't return any errors. 

The only thing that works is booting from USB with a version of Windows PESE... but that makes my hard drive (SSD) disappear both in Windows and in the BIOS. 

Restoring the BIOS to factory settings makes the hard drive reappear, and the LiteON SSD is available again to boot from. Still doesn't work though. 

Any advice on what to check/test? Or any solution to this issue? 

Thanks!!