The problem you most likely have is that your thermal solution is not put on properly. I suggest you get some Artic Silver and redo that paste correctly.
Here are
Artic Silver Instructions
YOu have to clean off the old before you put on new, so please follow those directions very carefully and that should help you a lot IMHO. Pay close attention to the comments about how much you put on, because too much can be as bad or worse than not enough.
What happens in this instance (well, that is what I think) is that your paste is not on correctly or that factory thermal pad (they are not very good) is not doing the job, so your computer just keeps heating up until it gets too hot and shuts down to prevent your CPU from burning up. I would not try to run it any longer until you get that issue taken care of.