I sent in my macbook pro 15" about 2 weeks ago to have its logic board replaced because of screen flickering. A couple days after I got it back, it started giving me 3 beeps on startup. I finally was able to get it started somehow and its been running fine untill today. It started giving me the 3 beeps again. I know this means there is something wrong with the ram. I opened it up and switch the RAM and it started. I went away for a couple minutes and when I came back there was a message saying that I had to shut it down holding the power button. When I tried booting it back up again, the beeps came back.