Suddenly my PC shut off by it self

Can you explain how the exact way it shut itself off? Does it restart? Or Shutdown? Does it happen in random and other details will help me know if I can solve your problem or not.

There could be many possible reasons. Do you see any blue screen before going off? If yes it should be a problem with RAM change it. Also check your smps, if it is getting heat and unable to the load it will turn off. If the problem is not resolved try some technical related forums they would help you resolve it however it is advisable to give a background about the problem like the configuration of your PC, how old it is, how many times it occurred etc.

I had the same experience with my PC. I have send it to our IT and first they told be that it has a problem with the power button so they had it fixed. After just a month it broke down again and this they can't open it even the hard drive. They said it's the hard drive and so they have to replace it with a new one. Problem is some of my recent files are not yet saved and I don't have copies of some of my applications there. I am still waiting fro it to return here. They said it was fixed but the documents are not recovered I hope it's not the same problem as yours.

Your hard drive may be overheating. Every few months I take the cover off my hard drive and clean it with a vacuum cleaner as it collects lots of dust over time which makes it over heat.

Your harddisk might get a problem. My computer used to be like that also and blue screen appears...however it is restarted and turned to normal, luckily... Better you should ask some computer technical person who can fix it for you. Good luck!

Have you said something not nice about your PC? Perhaps it read it and is unhappy? Ok, maybe it is not that. I can think of two possible reasons. One is conflict and the other is limitation. If your apps are many or large it might help to add more memory (ram) or uncheck things so that apps are not running in the background. Look in msconfig if you have a *microsoft windows machine, somethings you may not even be using. Another possiblity is a program has a conflict and crashing shutting down the system. This might be hard to find. You would see a difference when the app is running or not. Updates or refreshing the os are answers to continuing problems like this. How long has this been happening? That is a question that sometimes let you isolate an issue. Maybe others have other thoughts about shut off's.