Why does my computer stop out putting display??

[Vortex Hawk]

Twice my pc screen went completely black and looked. One time it shut down and one time it kept on running with a black screen.

At first i thought there was a lot of dust built up and my cpu might be overheating as i havent cleaned it in ages.

I dont think my graphics card is overheating as i monitored the temperature and it was below 40 degrees.

Whats wrong??

Also right before the screen went out it froze for about 2 secs.

It doesent happen when im on the desktop.

 

[nooneisback]

Does it stop working randomly or in some specific situations?