Need some help with computer overheating.

As a preface: I apologize for any peasantry you may witness in this post.

With that out of the way, lately I've been having trouble with what I assume is my heat sink.

Suddenly my computer will turn off, then within moments turn itself back on. I can only assume it's the computer overheating, but I don't really know if that's true.. Since the tower, cpu, etc., all still feel cool to the touch.

I opened up the tower, vacuumed out dust from the heat sink, propped open a window, and it still turns off at seemingly random times. So, glorious master race, I need your help.

EDIT: Checked the temp with an application- Looks like the temperature is steadily normal. I'll see what happens when I run something like LoL or Skyrim.