What to do if Windows won't start

In this article we will show you how to identify the problem when Windows is not booting and how you can fix it.

1. Windows 10 Startup Repair

Windows 10 comes with a built-in Startup Repair option that can scan and repair missing or damaged startup system files.

The fastest way to get to Startup Repair is to shut down the PC during startup three times. Typically, you do this by simply holding down the PC's power button. So hold down the power button of the PC while it boots three times in a row and the fourth time the PC loads Windows 10 Startup Repair.

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Alternatively, you can use the Windows 10 installation disc or create a Windows 10 recovery drive.

Once you have your recovery media, insert it into your PC and restart your PC. It should boot directly to the recovery media. (Otherwise, you should get the option to select the recovery drive while the PC is booting.) Click “Next” on the Windows Setup screen, then “Repair your computer”.

This will open the boot options where you can troubleshoot many Windows issues. Go to “Troubleshooting -> Advanced Options -> Startup Repair”.

When you click on “Startup Repair”, Windows will restart and will scan your PC for any system files it can fix. (Microsoft account authentication may be required.) If it finds a problem, it will automatically fix it.

2. Reset your CMOS

Resetting CMOS restores BIOS settings to factory defaults. This shouldn't have any negative effects on your PC and can actually 'cause' Windows 10 to restart.

You can usually reset your CMOS from your BIOS (which you access by clicking F2F8deletekey or similar as your PC is booting).

If you don't find the option there, turn off the PC, unplug it from the mains and try to hold down the hard reset button on the PC for about five seconds. After that, check if Windows starts.

3. “Windows failed to start” 0xc00000f

One of the most frequent error codes associated with Windows 10 not starting is the code above. The most cited reason for this is an error in the BCD (or boot configuration data).

O Windows falhou ao iniciar o Cmd de reparo de inicialização

The best way to fix this error is by repairing the BCD. Follow the instructions in Tip 1 until the point where you click “Repair your computer”.

Now, instead of going to Startup Repair, go to “Troubleshooting -> Command Prompt” and type the following commands:

bootrec / FixMbr bootrec / FixBoot bootrec / ScanOs bootrec / RebuildBcd

After the final command, type exitCommand Prompt, press Enter and restart your PC (without installation media inserted).

4. Check the motherboard connections

If you get a completely blank screen when Windows tries to start, then – if you're reasonably confident – it might be worth taking a look inside to make sure all the hardware is seated as it should. Here are the main components you should look at.

  • Memory / RAM: the RAM comes in the form of small, thin sticks, which can be easily dislodged if you've dropped your computer. Modern laptops usually keep the RAM in a bay at the bottom, which means you don't have to open everything up to take a look. Open your RAM compartment (or PC tower), take out the RAM and insert it back in to make sure it is securely connected.
  • Operating system hard disk: Another possibility is that the main Windows hard drive has been disconnected from the motherboard (or power supply). Press down on the SATA cables firmly and make sure it is also connected to your PSU.
  • PCI-E cards: it is less likely – but still possible – that a disconnected GPU or other PCI-Express device could be the reason your Windows 10 desktop fails to boot. Make sure everything is connected correctly.

5. Check external flash drives and disks

Your PC can be configured to prioritize booting from an external drive, which means that if you have another operating system or recovery drive on a USB stick and that stick is connected to your PC, your PC will try to boot from it.

If that external storage device is connected, Windows may try to boot from it, but fail because it does not have the correct device attached containing the recovery files. Remove all external storage devices before starting Windows and see if that helps.

6. Windows Boot Record Errors

Boot registry errors are the main cause of Windows not booting but luckily they can be fixed easily using a few command prompt commands. You can refer to this guide to troubleshoot boot record errors.

7. Use safe mode to resolve the issue

Whenever I face some Windows issue that makes the operating system inoperable, the first thing I do is go to Safe Mode. Safe Mode can answer many questions quickly and also make solving them easier. In Safe Mode, Windows starts with the minimum required drivers and only the necessary boot system files, so a faulty file, program, or driver is unlikely to load in this mode, which makes it easier to identify and resolve the issue.

While there are many ways to access Safe Mode, now that Windows 10 is not booting, we have limited options. If you restarted Windows several times and it failed, Windows will automatically open the boot options. If for some reason it doesn't offer this option (very rare), you can do one of two things:

1. Restart the PC, and as soon as Windows 10 tries to load; remove the power supply or press and hold the Power button to force shutdown. Repeat this process three to four times, and Windows should automatically load boot options.

2. You can also try pressing the F8 key repeatedly while Windows tries to start and see if it loads boot options. This probably won't work on Windows 8/10 as the boot time is very fast, but on slower machines it might still work.

In the boot options, go to “Troubleshoot -> Advanced Options -> Startup Settings -> Restart”.


Once the PC restarts, you can choose Safe Mode from the list using number key 4.


Once in safe mode, you can follow the guide here to troubleshoot Windows. Listed here are the possible things you can do in Safe Mode to resolve Windows issues (including Windows failed to boot issue).

Last resource


If for some reason nothing helps you and you are sure that you will have to do a clean install of Windows 10 and lose all your data in the process, there is still hope to save at least some of your data.

You can boot from a Windows 10 installation or recovery disc (which we described at the beginning of this article) and when booting select “Troubleshoot -> Reset this PC -> Keep my files”. This will back up and save all files, documents, images and so on held in user profiles in Windows 10 (and the profiles themselves). Third party programs, games and so on will be removed.

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Felipe Santos
Felipe Santos is a Cloud and Security Architect, with experience in Windows Server, Cluster, Storages, Backups Veeam and Office 365 environments.



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