You can only do a repair install from within that Windows.
From the repair mode, you could try the Startup Reapir up to 3 times, but I've never know it to fix anything.
Alternatively, can you select Command Prompt and enter bcdedit |find "osdevice"
(That is a Pipe symbol before find and is the uppercase of \ )
If that cmd gives a partition letter for the volume then enter chkdsk x: /f using the partition letter instead of the x I've used.
I can't remember if that requires a reboot to dismount the volume but if it does and it can't execute, then boot up with a Win 10 install disk.
You may need to change the boot order which can be done by pressing and holding F2 as you switch on - this is for Win 10.
To boot with either a DVD or USB then you will need to disable Secure Boot if yours is an UEFI BIOS.
If you don't have Win 10 install media, you can create it from the following article, but read the instructions first as the steps differ for a DVD and an USB.
https://www.microsoft.com/en-gb/software-download/windows10When you have booted up and navigated to the Install screen, click on Repair your computer bottom left which will give you the repair options.
Again selecting the Command Prompt and entering that bcdedit cmd, enter chdsk x: /f using your partition letter which could be different this time.
If the chkdsk comes back clean or doesn't resolve the boot, then you are probably looking at a clean install.
Also make a note of any reported KBs in bad sectors as they could be the cause of the no-boot.
If it does report bad sectors, depending upon how many then it may be worth running the chkdsk cmd again with /r instead of /f
If that gets you back in then it will be prudent to create a system image in preparation for replacing the HDD.
A word of caution though if you have upgraded that HDD to 10 is that if you replace the HDD with a larger one and restore with that system image, then you will have the excess listed as unallocated space for which you will not be able to extend to the volume partition as that can only be done when the unallocated space is immediately to the right of C:
A Win 10 upgrade places a 450MB recovery partition in that position which will stop you from extending any unallocated space.
If you free upgraded the HDD to Win 10, during the clean install when you are prompted for a product key, use the option that you don't have one and the install will progress to activation.
