Hi,
The 24 character error code is a failure of the short Disk Self Test ( DST ) and would indicate that the Hard Drive is failing and needs to be replaced. This is also consistent with the boot issues you describe.
The drive on the link below is an example of one that would be fine for your notebook.
The procedure to replace the Hard Drive starts on Page 54 of your Maintenance & Service Guide.
You can just perform a clean installation of Windows 10 as detailed in the guide on the following link. Note: At the activation screen, select 'I don't have a Product key' - Windows will activate automatically once the installation has completed.
http://www.howtogeek.com/224342/how-to-clean-install-windows-10/
Regards,
DP-K