I was doing an update for my macbook & it required me to turn off the computer and then restart it by holding down the power button until a screen came up. Well I did that but then the power ran out (which was my fault) and now when I try to turn the macbook back on it just gives me a black screen even though the the little while light is on. I tried the troubleshooting tips from apple support & I tried rebooting from the install cds but nothing is working. Please help!