MacBook Pro (Mid 2012) keeps shutting down randomly

I got a 13 inch 8GB MacBook Pro (mid 2012) two years ago before going away to college. It has worked wonderfully, but lately the computer shuts down randomly. Sometimes the screen flashes in a weird way, and others it just goes black. I don't use my computer for anything other than browsing the internet, listening to music, and typing papers. Any suggestions as to how I can fix this before I go back to school later this month?