MacBook pro won't start up

My macbook keeps shutting down and then being unable to boot up again. Whenever I try to turn it on the sleep indicator light flashes three times, but it doesn't beep anymore.

I assumed that this was a ram issue, but I use factory ram cards which have worked for me for a few years now.

Typically just reseating the ram allows it to boot again, but having to do that almost every day is becoming a pain and it is becoming unsafe to do any kind of work on the computer because it can crash at any time.

Often, when I'm using the computer it will freeze and then a few lines appear on the screen for maybe one minute before shutting down and being unable to start up again.