Does your Computer Turns Off Randomly?? And you have no clue about what is happening to your system?? One of the main reason for this problem is the high temperature inside your CPU, i.e. the processor , Graphics Cards etc. will be working at a high temperature. Then your system Turns Off inorder to protect itself.
SpeedFan freeware programs monitors the CPU temperature and increase the fan speed(rpm) in accordance with the temperature thus prevent overheating. SpeedFan also monitors the different voltage levels of your computer. The size of SpeedFan is around 1.8 MB.

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SpeedFan is a freeware program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. It can access S.M.A.R.T. info for those hard disks that support this feature and show hard disk temperatures too, if supported. SpeedFan can even change the FSB on some hardware.

At the lowest level, SpeedFan is an hardware monitor software that can access digital temperature sensors, but its main feature is that it can change fan speeds according to the temperatures inside your pc.