HP split 13 x2 - does not detect an operating system. (3FO).

[P_Fitz]

As above it does not detect an operating system.

[BeemerBiker]

You need to determine if the disk is bad or if it is simply corrupted and needs a startup repair.

Turn the power on and tap the ESC key to get into the diagnostics menu. Press F2 to run the UEFI diagnostics. Can you pass the memory and disk test? Do not allow any updates or repairs if disk or memory fail, especially a BIOS update.
If you can pass the memory and disk test then you need to do a startup repair.
If just the disk test fails then the disk needs to be replaced. If under warranty and no backup then you might want to request the original disk be returned so you can extract important files.


To do a startup repair you need boot into windows recovery mode. First read this article about safe mode.
Skip down to 'Enter safe mode from outside windows'. If f11 does not get you into system recovery then try turning the power on and off three or more times in a row.
When you get to advanced options select 'Startup Repair'

If the startup repair fails then try the restore point.

This video describes how to use a restore point
https://www.youtube.com/watch?v=sixGAIiPTlE