Macbook Pro (mid 2010) shutting down upon boot up Here is my question.  My macbook pro has been acting crazy for a while, shutting down unexpectedly daily.  Every once in a while it will work for a day or two but eventually will start shutting down again.

I took it to an Apple certified repair shop and after tons of cash spent...
I sent it directly to Apple and they replaced something for $350 - it was over a year ago and I can't remember (yes I am a moron).  It worked for a while and lo and behold started shutting down again.  

I ran the disk thingy where it checks the hardware and it said there are no issues.  Yay! But, now what to do?  

I can log in under the Test user the Mac dude set up at Apple shop.. and on here, where there are no files, everything is kosher and working smoothly.  No shutting down!

So, I am guessing its a memory issue?  But I checked that on a good day and everything seemed fine. 

Question is how do I get in to the other user to determine this?  is there a way to access the files from the other user through this alternate user?

I am at my wit's end -thanks for any help .
Could be the keyboard, where the power button is not working right (my sister had a MacBook Air that did this). Massage and blow compressed air into the power button and see if that helps.