Auto shutdown

ive been trying to help this guy fix his computer but he says he auto shutdowns i asked him why but he dosent know so i just assumed he was overheating so i told him to boost up the fan speed and see if it runs longer without crashing no luck though here are the specs he said he is using the stock heatsink

Case - Sentey Optimus with 3 120mm fans and 1 200mm fan
Motherboard - P55M-GD45
Processor - i5 760 2.8 ghz Quadcore
Graphics - MSI 7770 1gb
Ram - Gskill Ripjaws 1x4gb
Hdd - 500gb 7200 RPM Seagate (This is the only used part)
Power Supply - Solid Gear 80 Plus 400 watt

did you try changing out the psu they die firstĀ