Why does my macbook pro shut down after a few minutes?!

I've tried to bring this up with support among the many other truly OBNOXIOUS issues with my less-than-one-year-old macbook pro, but no one seems to be able to help me. So, I figured I'll ask here- call it a hail Mary. WHY on God's green earth does my macbook shut down after only a 30 minute or 1 hour break? I shouldn't have to leave some other program open with unsaved changes in order to be able to come back and pick up my work where I left off. Even having done so, just now I had a process going in another program that takes 245 minutes to complete. I left it running and even left unsaved changes in a word document and when the computer attempted to shut down it stopped the process of the program I was waiting for. 245 FREAKIN MINUTES wasted! I'm a big girl, I don't need help shutting off my toys. How do I stop this STUPID process from ruining my productivity on a daily basis???