Its a common sight to find laptops running Windows 10 caught in an infinite repair loop. While the OS is generally stable, if broken, it is hard to repair because it hardly gives an opportunity for users to intervene and take appropriate action. Lenovo laptops in particular seems to particularly afflicted after BIOS software updates.
The first time my Lenovo 520 was caught in the repair loop, I was totally caught off-guard. To me the error messages seemed to point towards bad-sectors in beginning part of the HDD. Such errors can make it impossible for the OS to read the partition table, master boot record, boot files or even the file-allocation table pointing towards critical operating system files.
I ended up formatting and re-installing the operating system just to diagnose HDD errors instead of straight away sending a brand-new machine for repair to Lenovo. Surprisingly, while I was able to format and install the OS, it refused to boot the second time and got caught in a repair loop.
Poking around the BIOS settings revealed the underlying issue and helped me solve the problem. The next time the same error occurred, it was after a BIOS update from Lenovo. This time I applied the BIOS settings fix straight-away and the problem was resolved like magic.
It turns out that every-time a BIOS software update is performed using a package from Lenovo, the BIOS settings are reset to default. Laptop BIOS hardly have any configurable features and most users have never even attempted to enter the BIOS to poke under the hood. Windows 10 also makes it incredibly hard to enter EFI-BIOS settings irrespective of how quick fingered you are. You need to wait about one-hour for five cycles of Windows 10 Repair attempts to fail before you are presented with an option to launch BIOS settings.
Particularly in my case, after a BIOS reset, the SATA mode is changed to Intel Rapid Storage Technology (RST). Theoretically, Intel RST helps speed up program loading from legacy disk technology such as HDDs by prioritizing the allocation of sectors that are closer to the spindle, to programs that are executed frequently. This way the seek time to the files is greatly reduced. The Intel provided RST device driver works with Windows 10 to accomplish this in the background.
On the other hand, a legacy HDD (like the 2 TB Seagate HDD on my laptop) may fail to locate the requisite files at boot if Intel RST is enabled in BIOS. In my case, it appeared that while booting process started, it could not complete as critical files such as Windows Loader could not be located on the disk.
Changing the BIOS settings from Intel RST to AHCI immediately resolved the issue. Upon boot, the computer acted normally and booted successfully without any further ado.
Please study the image below for an illustration of what setting I changed in the BIOS to get the machine to boot successfully.
I personally know a student who was crestfallen when his brand new Lenovo Laptop stopped booting after a BIOS update. Being a non-technical person, he tried what Windows suggested and eventually gave the laptop to the service center. The service center kept the laptop for one week, formatted it to re-install the OS afresh and returned it with complete loss of data.
If you are a Lenovo Laptop user and face this issue, perhaps you can try the above approach to see if it helps. This solution may also work for laptops from other brands such as Dell, HP etc.