How long does it take for the shutdowns to happen? Are there any error messages or messages at all when you start the computer back up? Are you trying to do something in particular like gaming when the laptop turns off by itself. Is the turn off immediate, or does Windows close out programs before turning off?
Sorry for the list of questions but it will help the forum get a better grasp as to what the problem might be if you answer them all as detailed as you can.
If for whatever reason you think it is a manufacturing defect though, go ahead and use your store return policy and ask for a return or exchange. Sometimes there might be something simple wrong, or it might not be broken at all, but peace of mind is something that is worth...