If a critical Windows system process fails to run properly, your operating system will crash and display a Critical Process Died Stop Error 0x000000EF or Blue Screen on your Windows 10/8/7 computer. This happens because the process which was needed to run the Windows operating system ended abruptly for some reason.
There is not much documentation on this on any Microsoft site. A post however simply states that:
The CRITICAL_PROCESS_DIED bug check has a value of 0x000000EF. This indicates that a critical system process died.
Now if you receive a CRITICAL_PROCESS_DIED error message, here are some of the things you could try and see.
1] Run the Hardware and Devices Troubleshooter and see if that helps. Run the Driver Verifier Manager and see if it helps troubleshoot, identify & resolve the device driver problems.
2] Run sfc /scannow or System File Checker to check for and replace corrupted system files if any. If you are unable to boot to desktop, you may run System File Checker in Safe Mode or Offline.
3] You may also want to run DISM to repair a corrupt system image.
4] Open Devices Manager and see if any devices are marked with the exclamation point. Update your Drivers and see if that resolves the issue. Did you install any new device or hardware recently? Disable, remove or uninstall it and see if it helps.
5] Perform a Clean Boot. When you start the computer in clean boot, the computer starts by using a pre-selected minimal set of drivers and startup programs. Clean-boot troubleshooting is designed to isolate a performance problem.
6] If the problem started appearing recently, use System Restore to restore your computer back to a good point and see if it makes the problem go away. If it started after you updated your operating system, you may want to stop that particular update from being installed, and report the problem to Microsoft.
7] Disable Sleep and Hibernate in your Power Setting and see if it helps. You will get these settings in Control Panel > All Control Panel Items > Power Options > Edit Plan Settings. Use this process to disable Hibernation if you had earlier enabled it.
8] See in an update to your system BIOS or firmware is available.
9] If you are unable to boot into Windows, you may want to run Startup Repair from the Advanced Startup options.
Once you are able to access the desktop, you may continue with troubleshooting the issue.
If you are unable to boot into Windows or to the Advanced Startup Opions, then you may have to use a Windows installation or recovery disc, to carry out your troubleshooting.
10] Check the System Log in Event Viewer and see if and error messages point you in the direction to troubleshoot.
11] Run the online Windows 10 Blue Screen Troubleshooter from Microsoft is a wizard that is meant to help novice users fix their Stop Errors. It will help you fix this Blue Screen error and offers helpful links along the way.
If nothing helps, check this post which shows you some generic ways on how to troubleshoot Blue Screens in Windows 10.
All the best!
See this post if you receive a Kernel Security Check Failure error in Windows 10.