What are the possible cause why computer shut down randomly?

The most.probable reason.... Get the cpu cleaned. Random shutdown occurs because of thermal shutdown designed in the system. Once the operating system and bios detects the cpu.temperature above.normal, it shuts down the system foe safety reasons. Processors are thw most static parts in the computers, hence vulnerable to dirt n dust. There is a thermal paste applied on the processor to fill the air gap between processor and its heat sink. This paste gets dry with the passage of time and the dust cover over the heatsink makes it a hot quickly. So cleaning these parts regularly will keep your system healthy........dont neglect the coolong fan... ;)

Mostly over heating makes PC shutting down. Hardware incompatibality can also be a cuase. CPU thermal paste if not applied properly can also lead to same problem. A heat sink and cooling fan is also required to keep CPU cool and working properly. 

mostly system or cpu temperture so i must replace the cpu fan, but u can face this problem also if the power supply is about to die so u must check it too

firstly remove the side cover and and see if the cpu fan is working or not and see if there is any blockage due to the dust in the fan. Remove any obstruction and apply the thermal paste on the cpu. If problem persist then it could be due to the swallen caps on the motherboard as well. And dont miss the PSU as well make sure if the PSU Fan is in working order also.

computer randomly shuts down becaue of voltage if voltage good then hardware like proceesor over heat or hard drive dump or ram dump it can also caused by bios error /

Due Some hardware Problem

Some Virus Infection

Ventillation of the system is poor and sometimes processor when reach the hottest temp it will shutdown the whole system to don't have damage to hardwares.

 drivers are bad

or

some hardware is bad

or

 PSU is not powerful enough

or

make sure the heat sync/cpu has thermal paste on it

you have to change thermal every8 month