my macbook pro won't turn on

I had used it two nights ago and it was fine. I have just updated to snow leopard a couple weeks ago. Everything was working fine. I wake up this am and it won't turn on. I manually press and hold the power button and it makes that noise like its turning off. I tried to turn in back on, and the grey light on the button turns on and it sounds like its going to turn on but then the grey light stays on and the screen is blank and there are no other sounds. I took the battery pack out and put it back in again and it still doesn't work. HELP