The 3 red lights usually just means it over heated. Mine did this all the time, and by pulling it out of my tv stand and standing it on its side, this fixed the problem Or you can get one of those fans that plug into the back. When it's got a full 4 red lights that means it's the red ring of death and you have to send in to have them repair it.
That's known as the ring of death. Happened to mine before and I took it to get it fixed and unfortunately it couldn't be. But also in many cases other people have been able to get theirs working again! Take it to get repaired. Good luck.