The precise problem
The screen turns off the display suddenly, and does not respond to the mouse or keyboard.
What actually happens??
When I am working on my PC (OS - Ubuntu 14.10) suddenly without any reason my computer slows down. Within few seconds the monitor gives the warning and then turns off - it works in the same way when the operating system is locked with the shortcut keyboard combination "Ctr+Alt+L". But then in this case which I am mentioning the command to lock the screen is not given. And normally when the screen is locked, then after pressing any key on the keyboard or even after simply moving the mouse, the screen turns on and the system asks for the password of the account which is locked. In the problem I am mentioning even that does not work. My PC does not respond to either the mouse or keyboard. At the same time if I am playing the YouTube and listening to something, it keeps playing, and I can hear the audio although there's no display.
I have not found the answer anywhere.
This is the fourth time this happened in the last two days, so I tried to search for the solution here. I found a similar question here, but there's no answer for the question. There are a few comments which are not addressing the problem, so I tried to repeat the question but with as much clarity possible. Note: It is not about "screen turns off after inactivity". I am actively using the computer when the screen suddenly turns off.
Important addition: After I posting this question, I have encountered a similar problem. I encountered it especially while watching videos on YouTube. I found a similar question asked here. The only difference is, I have experienced this problem continuously for the last hour while watching videos on other portals too.
Addition: Found the somewhat similar question here Yet my question is little different from all the 3 related questions I have posted here. None of the question is answered yet.
Addition: There seems to be some problem with Chrome. I tried using Firefox as suggested here but I do not think that it is a proper solution. I prefer chrome. so haven't got answer yet.

