If your computer turns off without giving any prior notice so this is often related to the heat matter. Today many computers turn off or mechanically reboot if the computer, processor, or other device in your computer gets too hot. You can also hear about the irregular noises which may be coming from your computer in recent times this noise make also result in weakening of computer.
For this reason first examine the fan on the power supply which is working by inspecting the back of the computer and checking that the fan is working very smoothly. Also confirm that the fan are working properly and/or if your BIOS monitors the RPM of the fans then enter the BIOS and also see to it that the BIOS does not result in any errors.
It is very much a good idea to verify it with the computer processor heat sink is properly connected to it or not then connect it properly other wise it will result in over heating of your computer processor and causing the problem.

There may be any failure of hardware factor in your computer which is causing your computer to do surprisingly turn off without giving any notice in advance. If you have recently added a new hardware device to the computer, then remove that device to make sure it is not causing your issues.
Before uninstalling the hardware, see to it that you are not been encounter by this issue because of the hardware conflicts by viewing Device Manager for errors.
If you have not recently installed any new hardware into the computer, the next best solution to determining if this is a hardware issue would be remove any hardware on the computer that is not needed. For example, remove your modem, network card, sound card, and any other expansion cards that are not needed for the computer to operate. Run the computer without these cards to see if they are the cause of your issue.

I think your computer is been attacked by the virus so that it is so designed in such a way that to shut the computer or turn off it. If the result from the computer seems to be turning off while running a program then it seems that it is been infected.
If there is a virus in your computer then see to it that the virus scanner which is in your computer is up to date updated for scanning and removing the virus from the computer.
Which will help you in solving your problem of turning off.

If your computer is rebooting, then it likely to be see that the computer is undergoing Microsoft Windows operating system related issue which are unable to be explained. For making help in this case, please try the below steps.
1. Reboot the computer and enter CMOS setup as the computer is booting.
2. After you have loaded the computer in CMOS setup, let the computer sit.
If the computer does not reboot while leasing the computer sit in CMOS it is likely that you are in truth experiencing an issue with Microsoft Windows and if no change then you reinstall your version of Microsoft Windows in the computer.

If you have done the reinstalling of operating system but still facing the problem when it turn off abnormally and is very much likely that the other hardware will fail in the computer. This is mainly caused in RAM, CPU, Motherboard and the power Supply.
If you have extra available parts or have a friend or co-worker with a similar configuration that is willing to allow you to test the hardware in your computer, try swapping these parts to determine if they are at fault. Otherwise, you will need to have the computer serviced.