yea, my new computer that i built, keeps shutting down while doing cpu intensive stuffs.

i have seen it as high as 120 degrees c before it shuts off, but it also shuts off around 60 degrees,

is this a o\ver heating problem or is this because of my power supply not being big enough?

i only have a 650 watt btw and my computer wont even turn on if i put my other video card in...