When certain actions done in a game, pc proceeds to shut of!

[CanonMp]

So recently i decided to buy a copy of csgo on my new Steam account because i hadn't played in a while. I launched the game perfectly fine and played a bot game. I then tried to play with friends and that is when my pc just shuts off. I left my pc alone for 2 days and tried again and it still shut off. Today I bought and ran NBA2k17 everything was fine until it actually loaded into a match. This also happens with many other games.
Any information helps, here is my speccy info. Also upgrading to 16gb of RAM soon.

Operating System
Windows 7 Home Premium 64-bit SP1
CPU
AMD Phenom II X4 980 53 °C
Deneb 45nm Technology
RAM
6.00GB Dual-Channel DDR3 @ 668MHz (9-9-9-24)
Motherboard
ASUSTeK COMPUTER INC. SABERTOOTH 990FX (AM3r2) 39 °C
Graphics
ASUS VH238 (1920x1080@59Hz)
4096MB ATI Radeon RX 470 Graphics (Sapphire/PCPartner) 38 °C
Storage
931GB Seagate ST1000DM003-1ER162 ATA Device (SATA) 37 °C
Optical Drives
ASUS DRW-24B1ST c ATA Device
Audio
AMD High Definition Audio Device

 

[batmanx999]

had a similar issue a while back, turned out to be the power supply after i literally tried everything i could think of.

http://www.tomshardware.com/answers/id-2914343/shutting-randomly-gameplay.html

maybe some info from that will help you.