Question Pc won't freeze if i play games !?!?

[ZaZaMaZa]

My pc won't freeze if i play games . I can play for hours rly demanding games and it won't freeze . The temps are normal and else . But when i leave it alone in desktop it will freeze if i leave its side . !???
I can't leave nothing do download ,it's realy bugging me ,
Please help

 

[rgd1101]

full system spec? include make and model of the psu

 

[ZaZaMaZa]

Lenovo Mahobay M92p
i7 3770
GTX 970 Asus Strix
8 gb ddr3 Crosair Vengance 2x4 GB kit
Thermal Master 420W ATX 12V
i did the stress test in FUrr in 720 p FHD 1080p no probs