It's almost bedtime for me! Run Windows 10 Disk Manager:
+
R then type
Diskmgmt.msc,
- Make sure that there are good views of the Upper and lower panes showing : Volume, status, etc., details - you may need to make it full width - e.g.
We know nothing about the state of the recovery partition yet. Once we have converted the OEM recovery partition type to 07, we can give it a drive letter and view in Explorer, but Windows is not exactly straightforward how to do that. It can be done in diskpart, but we don't want to go there yet. Tomorrow!
My personal opinion is to wipe the disk, install Windows 10 with the digital entitlement the OEM Windows 8.1 has given the machine, and download the drivers and HP software for the machine, but don't install anything that is not absolutely essential to make all the devices work properly - Chipset, Storage, Graphics, Sound, Network, Cam, DVD-RW and Card Readers etc. if present, should all be working properly in Device Manager.
You can transfer the Windows 10 license you bought to another machine separately.