This can be hardware (most likely) or software related. To make sure reboot your computer in safe mode and see if the problem persists. If it does you can be 99% sure that you have bad ardware. Try the following steps to resolve the problem:

Check your power supply - it is the most likely culprit, if you power supply is bad you’ll have to replace it.

Faulty video card - remove your video card and see if your computer shuts off again. If it doesn’t then your video card is faulty. Try downloading the latest drivers and see if that fixes it, otherwise replace it.

Cpu overheating - clean your CPU fan, and check if it works properly, if it doesn’t then simply replace it.

Bad RAM - if you have two (or more) RAM chips in your PC remove them one by one and see if the problem persists. IF your RAM is bad you’ll have to buy a new one.

Spyware, viruses - update your anti-virus software and run complete check on your PC, download Spybot - Search & Destroy and check your computer for spyware.

Hope that helps
THT