Question: I have discovered this problem with my Laptop, today itself. No matter what the environment, app, screen is, as soon as I press **CAPS LOCK** key, the computer shuts itself down abruptly (abnormal shutdown, like power failure). 

It can again be turned on normally though, using power button.

I Googled a bit and discovered that CAPS LOCK is used as CRUISE control so it shuts down the laptop in-case it is not cool enough. My laptop is cool enough.

Following are the environments, in which I've tested this abnormal behavior of CAPS LOCK (abruptly shutting down my machine)

1. GRUB
2. UBUNTU 16.04
3. System Testing (F12)
4. Windows 8
5. Pressing CAPS LOCK on on-screen keyboard
6. External Keyboard's CAPS LOCK

My laptop is **Dell Inspiron 3542**. Thanks

Answer: 
I had exactly the same problem. In my case keyboard replacement in laptop (Lenovo ThinkPad T420) solved the problem.
I have a dual boot computer and both Windows 10 and Ubuntu have the same problem... touch the Caps Lock and you instantly shut off the computer. I had to start up RegEdit and go to: HKEY\_LOCAL\_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout
There I had to a enter a "Scancode Map" and put in the following 00000000 00000000 02000000 00003A00 00000000. That disabled my caps lock key completely. 

However that did nothing for my Ubuntu 17.04. There, I had to set up enter the following in the .bashrc and then in the Startup Menu (both).>> Setxkbmap -option '' -option 'ctrl:nocaps' 

With that I was able to disable the caps lock completely.