Computer Shuts Down Randomly? - 1

There's no heating problem. There's some kind of virus are running please follow these steps:

1.Install a new window after formatting computer.
2. Do not install any software or don't connect any pen drive or usb.
3.First step after installing fresh window is install an updated Antivirus(If it is purchased that will be best. You can use Norton/Kaspersky or Quick heal, these are very strong and effective antivirus.) and scan whole computer with it.
4. If any virus will detect remove it, and install other software which is require for your PC or laptop.
5. You will never face any problem or freezing.

It could be an overheating problem - download realtemp and msi afterburner. If your temps are going over 70 degrees or more the computer is probably shutting down for safety. I don't know what motherboard you have but some have temp monitors in the BIOS as well.
If it is overheating its more than likely that the fans to the CPU, GPU or case are clogged or that the thermal paste has degraded on the CPU or GPU and will need replacing. There are youtube video's that show you how.
If its not overheating then remove all components and just try with CPU, GPU and one stick of memory in the motherboard (with mouse, keyboard and monitor attached). Then add any other components you have one by one. If the problem happens before you add extra components then check your wiring and consider buying a replacement motherboard or PSU.
Whatever you try, stay safe and make sure the computer is always switched off AND unplugged before doing any work - a lot of motherboards are still live even when switched off.
If all else fails, try reinstalling windows and the drivers for your motherboard, GPU and any extra's you have. Better to get them from the manufacturers site rather than disks as they'll have updated versions.

Could also be the power supply overheating and cutting out?

It shutdown without any warning message? You can install some tools to monitor CPU temperature.
You may need to check windows log to see is there any clue you can follow
Possible reason other than over heating
1. Memory error
2. Power
3. Motherboard
4.OS

Does it shutdown like as if you hit the shutdown button? Or is it your working on it and it goes "click" off? If it's the first scenario then it's likely a software issue. If it's the second, then it is more likely hardware. Have you tried re-installing the OS to see if it's something has gone wrong in Windows? Get a program like HWMon to watch your thermal levels in your computer and see if something is running way too hot. I'll give a link below. Could also be a bad power supply or power cabling. Make sure your power cables are securely attached to your system. To test a power supply though you would need proper testing equipment which few people have. Last would be is the motherboard damaged or failing? Hard to tell without tearing it down and testing the parts.