Usually it points to a buggy driver. Hope something in one of these articles helps.

https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/bug-check-0xef--critical-process-died

http://www.thewindowsclub.com/critical-process-died-error-windows

http://www.tomshardware.com/forum/id-3437065/critical-process-died-error.html

EDIT

Wanted to add this post that was here on Dell forum.

https://www.dell.com/community/General/Dell-XPS-9550-quot-Critical-Process-Died-quot-and-other-blue/m-p/5085430

This problem usually happens due to the following reasons:

• Antiquated software plus faulty drivers.
• Corrupt as well as broken files.
• Issues related to code such as memory house concluded, out-dated drivers, malware attacks, and more.
• Hardware issues like RAM, CPU, hard drive, and more.
• Operating system issues.

Try rectifying these problems to solve this issue.

I have found this easy guide which is on this problem. 

Is it a laptop? Is the battery old? Does it often occur when unplugged? It's probably because of a dying or faulty battery. Try replace a new battery. Better buy Dell battery...  Dell make it very unfriendly to 3rd party aftermarket battery....

I have a XPS15 9550, and my battery was dying and had this critical process died issue when on battery (i guess something like not enough battery voltage has caused the issue) I replaced a aftermarket battery and had tough time getting correct battery meter and soon after the battery became faulty. I got another one and no critical process died issue.

I have the error Critical process . But I can't boot up . I tried everything I can't even do a System reset .

Finally I decided to reinstall windows but I can't when put my USB and click on it Setup runs says no Driver with windows can be found.

I think the problem is when Critical process died a corrupted file must damage Drivers too. SO my USB is not showing on Windows Setup and I don't know how to fix this. Pls Help