Macbook logs me out within less than a minute of logging in.

My computer always shut off on me because I dropped my iPod on the back of the screen when it was shut, damaging something in the screen. I wasn't able to fix it due to financial issues. So, I learned to get use to it shutting off every once in a while. That being said, i recently downloaded bluestacks while Adobe Premier Pro, Google Chrome and a video player was on (I was working on an assignment) while I was installing bluestack, my computer screen shut off on me, so I held the power button until it shut off, and turned it back on. But when I logged in, it would only log me in for 30 seconds and go back to the login screen.

I really need help, as soon as possible! I'm currently working on an assignment and can't hand it in until I get it fixed.