Can I reinstall Windows 10 without using external devices?

[jhayzhee.jf]

My laptop (Asus L402S (that's what it says here) with added 500 GB storage, registered as D was running low on storage because it has plenty of junk files that I can't delete because I have to be an administrator. I must do it because updates are killing me, to the point where I can't even use my laptop anymore. My brother and I tried different ways to fuse C: and D: but no luck, so he worked on it, reinstalling Windows 10, resetting the device etc. Works well on first boot, but shows the same problem on the next boot.

Your PC needs to be repaired
A required device isn't connected or can't be accessed.

Error code: [A Mix of Letters and Numbers]



Press Enter to try again

Press F8 for Start-up Settings

Press Esc for UEFI Firmware Settings

 

[jhayzhee.jf]

MERGED QUESTION
Question from jhayzhee.jf : "Your PC needs to be repaired A required device isn't connected or can't be accessed"

My laptop (Asus L402S (that's what it says here) with added 500 GB storage, registered as D:.) was running low on storage because it has plenty of junk files that I can't delete because I have to be an administrator. I must do it because updates kept bugging me. My brother and I tried different ways to fuse C: and D:keeping everything intact, but no luck, so he worked on it, reinstalling Windows 10, resetting the device etc.He eventually managed to fuse the drives and reinstall Windows 10, but then comes the problem. Windows 10 works well on first boot, but shows a dialogue on the next boot that looks like this:


Your PC needs to be repaired
A required device isn't connected or can't be accessed.

Error code: [A mix of numbers and letters]



Press Enter to try again

Press F8 for Start-up Settings

Press Esc for UEFI Firmware Settings

 

[webworkings]

Only if you have a partition on the drive that has the original/backup files that you would need. If you don't have that, then you will need another way to install the original software/OS.