Why does my computer randomly shut down?

Question

Video cards

There is iron, relatively old
Motherboard gigabyte h55m-d2h
Processor Core i7 860
Video card MSI Radeon HD7770
While working in sketchup, during the rendering process, the video heated up to 100 and the computer went into protection, stupidly passed out. I opened the lid, cleaned it (although there is no dust, the thermal paste is changed regularly), with the lid open on the FullMark test, the video temperature rises to a maximum of 74 degrees, the V-Ray render also works stably. There may be a cooling problem, but all coolers are working and a couple costs extra...

Answer 1

Heating - 100%. Check CPU temperature.

Answer 2

The video card itself reduces the frequency and cools down. It looks more like BP.