When the screen shows this message, the machine has done all of the steps leading up to the firmware. Only the last step failed. Boot files take up a few hundred megabytes so your actual data is somewhere else on the drive, unaffected.
About half the time there is nothing wrong with the hard drive; something about where the firmware was told to look has changed. The other half the drive is failing. If there is a problem the BIOS should be able to point out what it is.
This is a smaller scope than it seems and frequently much less serious than it sounds.
By the time you see this message, many things have already gone correctly. That includes powering up; passing its self-test; initialising video and RAM; reaching the firmware; and searching for something to start from. All of those steps were successful.
When we say "it failed" we're talking about the very last step: there wasn't anything it had found that would have served as a usable boot loader. This could be due to the fact that the drive itself may be dead; however, it's also possible the boot order was altered, a cable became loose, a USB device was inserted, or the boot files themselves were corrupted on what would normally be considered a fully functional hard drive.
The significant implication: this message says nothing about your files. Boot files will never exceed a few hundred megabytes. Your documents, photos and all other forms of information exist in areas of the hard drive that are completely unaffected if/when the computer will not boot.
In the order in which you should investigate them, which is roughly the order of likelihood.
A USB stick, an SD card, a mobile device transferring files, an external hard drive. Firmware was attempting to load from something it thought might serve as a boot source, couldn’t locate one and quit. Remove everything and try starting up again — literally the most common reason.
Following a BIOS update, a CMOS battery failure, or after a firmware reset. This does not mean the drive is bad; it just means your machine is now looking somewhere else first. Look at the boot menu to find out where it's trying to go.
There was a problem with a Windows Update, there was a problem when shutting down the computer, or if you resized partitions but didn't complete the operation. The drive is still in good condition and all of its data remains intact – only the very small structures which allow your operating system to be loaded into memory were damaged.
It really is gone or so far gone that the firmware cannot read the boot sector. If your drive is completely missing from your BIOS, or the drive is producing some sort of noise; then this is where you are at.
None of those options will modify your disk.
Remove your sticks, cards, phone, and external hard drives — even some printers. Then turn on. If it boots now, the issue was just your unhooked device.
Typically F2, F12, Del, or Esc when you are starting up. Does the drive show? This is the only thing that will decide what happens next.
The drive is recognised and communicates, therefore the hardware is good. Make it the primary boot device and try again.
Absent from the BIOS indicates that no part of the system can "see" it; something is wrong with your connection, controller or drive. Don't run any repair tools since there is nothing to fix.
If you hear a new noise coming from the machine it has never made before – then none of the other considerations matter. Shut it down and proceed to the final section.
The key thing most people miss – and is often the complete answer.
There is a big difference between booting and reading. Your files are available where the drive works – whether the machine starts up or not: remove the drive and plug it into another computer using a cheap USB adapter; start-up the machine with a live-USB, and transfer your information. In either case the broken OS will be immaterial.
It is worthwhile doing prior to considering repairs. All three of these methods (Windows Startup Repair, a system restore or a reinstall) write to the drive, and if your problem is due to a failing disk as opposed to corrupted boot files, you will be adding hours of writing to hardware that may not survive it.
When the drive does not show in the BIOS or if there are some noises coming from it then none of the above apply — the data comes back through imaging on separate hardware. In Manchester that is from £300 +VAT after a free 48-hour diagnostic; however, if the drive is healthy but the computer is dead we charge it as just another short copy job.
The fact that the machine started up correctly, looked for what to boot with, and could find no usable items. That has absolutely nothing to do with your files. Boot files take up a few hundred megabytes and anything else on the drive remains untouched.
Remove all removable devices, including but not limited to USB keys, SD cards, phones, external hard drives etc., and try restarting. This is the most common thing that causes problems during a boot process and you can eliminate it within 30 seconds.
Go into the BIOS and check if the drive shows. If it does, that means there was communication between the hardware and the problem lies either with the boot configuration or possibly with some damage to the boot files. If it does not appear at all in the BIOS then that indicates a connection problem, controller issue, or a drive failure.
Boot issues have no relation to file integrity. Most likely your photos & word docs remain unharmed.
Before you do anything else back up your important data. Because both write to the drive and can harm the disk in question. If the disk is going bad the last thing you want to do is spend hours writing to it.
And yes it's usually straightforward. Simply remove the disk and plug it into another computer via a USB adapter, or boot from a live USB to access the disk's contents. At that point it doesn't matter what was wrong with the original OS.