Flashing 'A' light? (by 2 users)

Hi, I have had my D600 for a few months now and have had no problems until last week when the whole thing suddenly crashed and turned itself off. When I pressed the power switch to turn it back on the screen remained blank and only the 'a' light at the top of the keyboard flashed for a few seconds before the laptop stopped again. I though it was the battery but I have charged, recharged and replaced the battery but the outcome is still the same. I have tried turning the power on everyday since and there is still no power. When I phone help lines all people say is that they dont know what the problem is. Can you help? The problem is becoming really irritating as I have work to do and cant get it done. Thanks.