I can guess of 2 things. A font trouble, if it is not delivering plenty current can occur that a fast shutdown. And the source has fluctuations or loser as a result of overloading. If that is so, you accept to change the power supply. By the path how lots Watts is it? The 2nd thing that happens to me is a failure of HD, which does not rule it out. In short, whatever the case, it appears you'll accept to replace any element. Although as I always say, it is hard to diagnose from here.